Remove GitLab-related code before Artemis release 8.0.0

[b-fein]

Is your feature request related to a problem?

GitLab support will be removed with Artemis 8.0.0.
The internal classes have been marked as deprecated already.

Users should migrate to LocalVC using e.g. the PR #8972.

Describe the solution you'd like

Remove the code shortly before Artemis release 8.0.0.
Also remove no longer required documentation, container setups, and helper scripts related to GitLab.

Additional context

• Mostly an informational issue to users of Artemis that are not developers themself and therefore do not see the warnings during compilation.
• Not sure about the planned rough timeline when the 8.0.0 release is going to happen.
• I can help in the removal process.

[krusche]

Thanks for creating the issue. We do not have a concrete plan for the 8.0 release yet. We will soon create one. A rough timeline would be to finalize 8.0.0 in March 2025. The deprecations in the code are mainly to notify developers that they should not build new features in the related classes.