Signed-off-by: Nxiaolong.ran <rxl@apache.org>


### Modifications

Use the 2.6.1 version of the docs as the latest stable version

Signed-off-by: Nxiaolong.ran <rxl@apache.org>

### Motivation

Currently, when the official website 2.6.1 document is released, we should first let 2.6.0 continue as the default version, wait for version 2.6.1 to appear in the historical version, and then try to use version 2.6.1 as the default version. If we directly publish the 2.6.1 version of the document, the search function will be unavailable.

### Modifications

- Update versions.json

Signed-off-by: Nxiaolong.ran <rxl@apache.org>

### Motivation

Update 2.6.1 docs

### Modifications

- update 2.6.1 docs
- add 2.6.1 sidebars.json
- update releases.json
- update versions.json

* Update the site for 2.6.0

* Update the site for 2.6.0

* add versioned docs

* add new version 2.5.2

* change following guangning's comments

Motivation
After the search is available, set 2.5.1 to the top
Modifications
After the search is available, set 2.5.1 to the top

### Motivation

* Update website

### Modifications

* Add 2.5.1 release document

### Verifying this change

Local test pass

### Motivation

Apache Pulsar 2.4.2 has been done, but we can see that the stable version of the [website](https://pulsar.apache.org/en/) is 2.4.1. That was done intentionally to get around the website indexing issue. 

Currently, Apache Pulsar's website indexing uses the **Algolia** framework, which takes some time. In Apache Pulsar 2.4.1,  users are complaining the website search is broken, this is the problem.

So in release 2.4.2, we published 2.4.2 documentation but didn't promote it as the current stable. We will make sure the  **Algolia** index works before moving 2.4.2 as the current stable.

In next release, we can think about how to improve the website update process for a release.

### Modifications

- Update website stable version to 2.4.2

* Update website for 2.4.2 release
Signed-off-by: Nxiaolong.ran <rxl@apache.org>

* update website docs for release 2.4.2
Signed-off-by: Nxiaolong.ran <rxl@apache.org>

Update website for 2.4.1 release

### Motivation

Release 2.4.0 doc

* docs for 2.1.1-incubating release

* removing docs for sql

### Changes

- cut the documentation for `2.1.0` release
- update website to display versions