Consider deprecation and/or removal of the pr-diff-checker action

[tbouffard]

We are introducing a new pr-antora-content-guidelines-checker action which is more powerful and easier to improve. See #115.

With @benjaminParisel, we are planning to make the new action available and start using it in the https://github.com/bonitasoft/bonita-doc repository to ensure it covers all the current needs and work as expected.
When we will consider it as mature enough, we will apply it to all documentation content repositories. At that time, we will be able to remove the former action.

Implementation notes

This will be a breaking change requiring a new major version. We could do it as the same time as we implement #116

Usage of the pr-diff-checker action in bonitasoft repositories

Document content repositories no longer use the pr-diff-checker action. See https://github.com/search?q=org%3Abonitasoft%20pr-diff-checker&type=code
They are now using a shared workflow which relies on the new pr-files-checker action. See https://github.com/bonitasoft/bonita-labs-doc/pull/149/files

This is part of

• Remove duplications in the GH workflows: PR metadata checks bonita-documentation-site#422
• Tool: detect pages that don't include an AsciiDoc "description" attribute bonita-documentation-site#591

[tbouffard]

The action is going to be removed. All documentation content repositories are using the new action for a while.