### Motivation

jdbc sink treat all record as INSERT before #4358 , now it requires an indispensable action property which seems to be a break change, and we can deal records without any action property as INSERT.

### Modifications

treat action not set as INSERT action like before.

Fixes #4554 

### Motivation
Add a new deploy tutorial for new Pulsar Functions structure.

### Modifications
Based on the original functions-deploying file, re-adjust the structure and language of functions-deploy.

Structure of Schema Chapter: https://github.com/apache/pulsar/issues/4789

* add thread/process modes

* update the differences between thread and process modes

* update

* update

* Update examples, thread/process modes

* remove process and thread modes

* update

* Refine functions overview and structure

* keep old files and structure, add new ones

* Update

* add a note at the beginning

* create new files for the new structure

* remove two examples

* will create new PR for each of those files

* Update overview

* remove thread/process modes differences

the 0 size limit can't means "infinite" size quota

### Motivation
Continue the issues of #4782

### Verifying this change
Add the tests for it

* [Transaction][buffer] Add data ledger position in txn commit marker
---

*Motivation*

Add the data ledger position into the commit marker of the transaction log.

*Modifications*

Create a new TxnCommitMarker in the proto.

*Motivation*

Currently KeyValue schema doesn't support using AUTO_CONSUME.

This PR is to add this support.

This PR is based on #4836

*Changes*

- refactor a bit on Schema interface to support fetching schema info for both AutoConsumeSchema and KeyValueSchema before subscribing
- add AUTO_CONSUME support to KeyValueSchema
- add tests

* Add maven plugin for style checking. Fix some style violations.

* Fix issues shown by the style checker in the pulsar-flink module

*Motivation*

Currently fetching schema information is done synchronously.
It is called in netty callback threads and will potentially block
async operations.

*Modifications*

Make most of the operations asynchronously in SchemaInfoProvider.

### Motivation
The original PR https://github.com/apache/pulsar/pull/4770 is merged before I could give some feedback, so I just create a new pull request.

### Modifications
1. Refine the structure, remove some unnecessary info currently. Thus it is displayed to users as a complete guide. 
2. Refine the language part, make it clear and concise.
3. Though "upgrade ZooKeeper" is optional, could we add information for it? So users can decide whether they want to upgrade ZooKeeper. When they upgrade ZooKeeper, they know how to upgrade.

fix #4755 
Retention policy is used in Ledger GC and Topic GC.
Default retention policy is not uploaded to zookeeper, but it is getted from zookeeper when it is used.
So, if zookeeper doesn't have retention policy, we should load it from default config file.
In Ledger GC configuration, it's OK.
https://github.com/apache/pulsar/blob/075f28b71c8fd9259ce8e136dbb81c0629c3f271/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/BrokerService.java#L739-L742
But in Topic GC, do nothing.

s/is/it/

* Add develop part

* Add new site2/docs/functions-develop.md for new structure

* Adopt advice from Jerry

* Update Python and Go examples

* remove some tabs for Go

* add Go example in logger section

* remove Encryptiion at the end

* restructure Example in SerDe section

### Modifications

When submitting a function via REST interface, if user doesn't provide the function package or function runtime as part of function config, the function will get submitted and deployed to run but the typeClassName for the source will not be set causing a weird error in the function instance code

### Motivation

A message doesn't get automatically ACKed if there is the output topic is not set

* Simplified assert statements in the tests. Switch to usage of static imports in tests. (Part 1)

* Simplify assert statements in the tests and use the appropriate assert statements. Switch to usage of static imports in tests. Remove unused imports (Part 2)

* Process requests asynchronously on some REST APIs (3)

* Add async rest handler to API for expiring message on single topic subscription

*Motivation*

Add a few recent presentations to the resources page. They cover different topics:

- 2.4.0 release
- use case
- serverless
- spark + pulsar
- flink + pulsar

Add an independent Chapter for Pulsar Schema.

This is the first section—Get started.

### Motivation
Continue the PR of #4151

fix #4707 

* [Transaction][Buffer]Add new marker to show which message belongs to transaction
---

*Motivation*

Add new message type in the transaction including data and commit and abort maker in the transaction log.

*Modifications*

Add two new types of transaction messages.
TXN_COMMIT is the commit marker of the transaction.
TXN_ABORT is the abort marker of the transaction.

Master Issue: #4756

### Motivation

This is a continuation of https://github.com/apache/pulsar/pull/4765.

### Modifications

Added async rest handlers to the following APIs:
```
DELETE /admin/namespaces/{tenant}/{cluster}/{namespace}
PUT    /admin/namespaces/{tenant}/{cluster}/{namespace}/unload
POST   /admin/namespaces/{tenant}/{cluster}/{namespace}/clearBacklog
POST   /admin/namespaces/{tenant}/{cluster}/{namespace}/clearBacklog/{subscription}
POST   /admin/namespaces/{tenant}/{cluster}/{namespace}/unsubscribe/{subscription}

DELETE /admin/v2/namespaces/{tenant}/{namespace}
PUT    /admin/v2/namespaces/{tenant}/{namespace}/unload
POST   /admin/v2/namespaces/{tenant}/{namespace}/clearBacklog
POST   /admin/v2/namespaces/{tenant}/{namespace}/clearBacklog/{subscription}
POST   /admin/v2/namespaces/{tenant}/{namespace}/unsubscribe/{subscription}
```

* Added more blog posts in the resources page

* Added 2 more posts

### Motivation

Fix #4732 

### Modifications

Add options to rewrite the namespace delimiter, disable by default

Enable rewrite namespace delimiter can work well with superset:
<img width="1279" alt="superset" src="https://user-images.githubusercontent.com/12592133/61385412-f0f35700-a8e4-11e9-87b2-a31b62128b58.png">


### Does this pull request potentially affect one of the following parts:

*If `yes` was chosen, please highlight the changes*

  - Dependencies (does it add or upgrade a dependency): (no)
  - The public API: (no)
  - The schema: (no)
  - The default values of configurations: (no)
  - The wire protocol: (no)
  - The rest endpoints: (no)
  - The admin cli options: (no)
  - Anything that affects deployment: (no)

### Documentation

  - Does this pull request introduce a new feature? (no)

* Add Upgrade Guide to Apache Pulsar

*Changes*

Add a general upgrade guide to apache pulsar.

* Update the upgrade guide

* [Pulsar-Client] Add Producer Numeric Properties Validation

* Aligned deprecated and new Producer API validations

* Deprecated and new Producer API validations are being aligned

* batchingMaxMessages C++ API is being aligned with Java API

* batchingMaxMessages Java API Validation is being aligned with C++ API

* Review comments are addressed

* Fix broken UTs

* Convert anonymous functions to lambda

* Replacing lambda with anonymous implementation, because lambda cannot be mocked

### Motivation

`pulsar-function-go/conf` package apply `instance-conf-path` with default value `HOME_PATH+github.com/apache/pulsar/pulsar-function-go/conf/conf.yaml`, once function deployed, the running node may not have the yaml conf file exist, then go function will panic with `not found conf file` error. 

This PR changed the logic of config parsing, parse `confContent` first, then parse `confFilePath` if `confContent` empty.