Add option to suppress merge commits diff in showRevision

[rscurciel]

I create this PR to fix the issues mentioned in the PR#750.
The code changes are basically the same that in the closed PR but adding tests (thanks @anatoly-spb).

The issues are

• https://issues.jenkins.io/browse/JENKINS-20389
• https://issues.jenkins.io/browse/JENKINS-23606
• https://issues.jenkins.io/browse/JENKINS-36180
• https://issues.jenkins.io/browse/JENKINS-65932

The goal of this pull request is to add the option to suppress merge commits diff in the showRevision methods, the feature is disabled by default to maintain backward compatibility.

I plan to create a pull request in the git plugin too to add the option to use this configuration in the Polling ignores commits in certain paths extension once this is merged.

Testing done

I've run all the unit test and the steps specified in the Contributing document.
I've also tested it in Jenkins with git plugin installed too.

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 demonstrates feature works or fixes the issue

[rscurciel]

Hi @MarkEWaite I just wanted to check if there's anything else I could do to help move this forward. Let me know if any further change are needed.

Thanks!.

[MarkEWaite]

Hi @MarkEWaite I just wanted to check if there's anything else I could do to help move this forward. Let me know if any further change are needed.

Thanks!.

Thanks for asking. I'm working on other topics that are higher priority for me right now. It will likely be several weeks before I can look at this.