Remove the following plugins due to they are legacy and unstable releases.
1. sharding-jdbc-1.5.x-plugin
2. sharding-sphere-4.x-rc3-plugin
3. sharding-sphere-4.x-plugin (This is for RC1 and RC2)

To people who want to use these removing versions, you still could copy the plugins from SkyWalking's 8.6.0 release to the '/plugins' folder to activate, unless SkyWalking has some core level APIs upgrade. This is very rare to happen.

* support spring-kafka 1.3.x and add test

* add spring-kafka-1.3.x-scenario to github workflow

* change kafka-plugin FAQ

* add supported versions

* update CHANGES.md

* Add the plugin for mssql-jtds 1.x plugin.