[JENKINS-76185] Add GitLab merge request compatibility

[BartVerc]

As mentions in JENKINS-76185, I want to make it possible to use this plugin with Gitlab Merge Requests as well.

I would like to know if I missed something somewhere, as I am not yet familiar with this code base.

Testing done

I tested it by running all the tests by mvn test.
Did not yet test it manually.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[BartVerc]

@MarkEWaite Thanks for picking this up 👍

[MarkEWaite]

I will be on vacation for 2 weeks and won't look further at this until after I return. The plugin needs better documentation to show how to use pull requests as a parameter. If you can help with that documentation and can confirm that it works, that would be great.

[BartVerc]

Hi @MarkEWaite, I just tested this feature and added the documentation for a Gitlab merge request example. It worked as expected.

[BartVerc]

@MarkEWaite I think this is ready for review or merge. Let me know if something else needs to be done.

[MarkEWaite]

@MarkEWaite I think this is ready for review or merge. Let me know if something else needs to be done.

Thanks! It will likely be several more weeks before I can review it. Many other things are on my list.