Add options for what to comment build status on

### What feature do you want to see added?

First of all, thank you for this amazing plugin!

I would love to see options that enable us to specify in what context the plugin notifies gitlab about the pipeline status.
E.g. I'd like to only have this plugin comment on merge requests, but not on branch pipelines or tags.
Ideally this can be done per project as checkmarks inside trait "Log build status as comment on GitLab"

This would also remove my struggles with extraneous MR comments in GitLab like these, where comments are displayed from before the MR is opened (26 minutes ago):

### Upstream changes

I guess the GitLabPipelineStatusNotifier already checks which context it runs in, so it shouldn't be too hard to add options for this.

https://github.com/jenkinsci/gitlab-branch-source-plugin/blob/40b5f0e67cd36c3e8b925baf41b17f907ef32314/src/main/java/io/jenkins/plugins/gitlabbranchsource/helpers/GitLabPipelineStatusNotifier.java#L379

### Are you interested in contributing this feature?

I'm happy to help but currently cannot contribute code directly