* add logstash logback plugin

* add logstash logback plugin, set pom provided, refine logback doc

* refine logstash logback doc

* refine the comment

* remove the app_id that not related to SkyWalking

* remove tag @date for CI error: unknown tag: date

* add description for iLoggingEvent for ci warning: no description for @param

* Fix the zookeeper plugin has many nodes in the cluster case

* support version

* Support play 2.x 

* ADD: add operationName length threshold

* MOD:move operationName threshold to Config, simplified code

* MOD:update agent set-up document, clean code

* MOD:add agent.operation_name_threshold conf prefix

* Support op group name in agent config core.

* Provide core API for operation name grouping, rest template plugin update, and doc update.

* Fix doc

* Fix test case.

* Fix missing changes.

* add shuyun to powered-by.md (#3341)

* add shuyun to powered-by.md

* update powered-by.md

* Remove static method.

* Log4j2 support AsyncRoot print tid
Support AsyncRoot print tid of all versions of log4j2 2.1+

*  fix "DATA_BINARY" limit VARCHAR(20000)

*  slow sql long string trim

*  fix slow sql has long string

* Add more configuration and explainations.

* Add cached writer so we need not call whole method.

* Make writer volatile.

* Make writer to WRITER.

* Rewrite the writeFactory for add the cached writer and keep the unit tests stable.

* Give the default writer.

* Remove volatile.

* Update powered-by.md

* Update powered-by.md

Change order

* support ACL

* support digest only

* Fix TTL issue.

* Fix issue.

* Rename `getSecondTimeBucket` to `getRecordTimeBucket`.

* Stabilize unit test

The FileWriterTest creates files in the source directory(failed to
delete them due to a bug in the `deleteDir` method), making
them being checked by checkstyle plugin and failed to pass.

* Seperate compilation step

Add cluster etcd config to cluster.md.

* set Override is not working.

* Submodule update

* Add header.

* Check license header strictly

* Ignore header template

* Include more files to check list

* Refactor open edge.

* Make refactor works.

* Revert log back.

* Remove unnecessary codes.

* Open edge for all internal binding interceptors.

* Add document about JDK 9+ module.

* Change bytebuddy to 1.10.1(unreleased)

* Change document

* 1. Adopt the latest bytebudy changes(snapshot only), commit https://github.com/raphw/byte-buddy/commit/b60971156403ed8fba6124b8e424f0749917594a.
2. Remove disruptor by ArrayBlockingQueue, because Disruptor can't work in both JDK 8(1) and 9-12, if we don't add `--add-modules jdk.unsupported`
3. Doc update.

* Update README.md

* update gateway

* Add pattern logger to replace the easy logger.
* Doc update
* Support console log 

change `agent.span_limit_per_segment` default value to match the default value of `SPAN_LIMIT_PER_SEGMENT` in https://github.com/apache/skywalking/blob/master/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/conf/Config.java

* webflux

* Support undertow routing handler