Consider removing job rc-bugs and move the script to some other tool or dashboard

Salsa CI currently has a custom script check_rc_bugs.py that is run in the optional rc-bugs job.

This should probably be removed from Salsa CI. The purpose of a CI system is to detect regressions and prevent mistakes from getting into the code base. All tests should test things in the code base of the project itself, such as does the code build run properly or is there any other flaw in the code itself. The CI can also reveal problems in the code that stem from e.g. new versions of dependencies. However, the CI system should not be checking for some external things that are completely out of the control of the developer.

The rc-bugs job is an example of a fully external test that does not test the code itself. If the job is enabled for a project, and a RC bug is filed, every single pipeline in any 'mainline' commit by the maintainer or Merge Request submitted by any contributor will start failing. There is no point in making for example all Merge Requests pipelines fail from all contributors just because someone filed an RC bug on the package.

Perhaps it would be better to move the check_rc_bugs.py to the devscripts package (like we did with missing_breaks.py) and then ask e.g. dch to run it and issue a warning to the maintainer if they are about to upload a package without having a changelog entry showing that the RC bug was addressed. It is information that is relevant to the maintainer, and only the maintainer can really address it. The existence of a RC bug is not a responsibility for any random contributor submitting a MR, and should not fail all pipelines.