[feature] support GitLab for PRs and issues

[sinedied]

It would be nice if the --pull-request-comment, --pull-request-describe and issue related-options could also work with GitLab.

I'm guessing it would also need a gitlab helper, similar to the github one.

[github-actions]

This is a good starting point for a feature request. To help the developer understand the scope, could you elaborate on what specific scenarios you envision where these GitLab options would be used? For example, are you referring to automated PR descriptions, comment generation, or issue updates within GitLab? Knowing the intended use cases will clarify the requirements.

AI-generated content by issue-reviewer may be incorrect

[pelikhan]

I'm gonna need help from gitlab users.