This PR is based on the proposal from #6846, it does the following
- Change the format of the plugin help page
- Create an external file for each plugin type that will get included by the plugin
- Add a script to generate the PR on each plugin repo with the static doc
- Add a script `ci/ci_docs.sh` that will be used to generate the list of plugins that can be installed in logstash from all the available plugins from the community organization
This PR is the building block for change in https://github.com/elastic/docs-tools/issues/3Fixes#6941
**Motivation**: We have decided to rewrite the documentation generator to add more features
to our documentation and to fix some outstanding bugs.
This PR addresses the following problem:
- Hard to add new features to the code base.
- The code was tied with Logstash.
- No easy way to publish the doc for a single plugin
- The plugin author was not able to test their documentation changes
- The reported errors were hard to understand.
- No easy way to automate it.
- the minimal requirement on base classes.
Fixes#5720
