Motivation:

Review code styles with some bots automatically.

Modifications:

Set up ReviewDog in GitHub Action to review code style.

Add more check rules to checkstyle plugin.

Result:

Obvious code styles can be reviewed and commented automatically.

* Allow use SkyWalking plugin to override service in Agent core.

* Fix CI.

* Remove duplicate plugin load.

* Add test cases for new plugin boot service machanism.