Sync (or otherwise de-duplicate) project maintainer permissions with gitlab

Problem/Motivation

Per 📌 Subsystem maintainer permissions on GitLab Needs work there is some level of duplication between Drupal.org project 'maintain issues' permissions and the permissions on gitlab that allow MRs to be closed, retargeted etc. It sounded from @drumm's comment on that issue like the eventual fix might be to make gitlab the source of truth, and sync this back to Drupal.org for projects, once issues are migrated. Opening postponed because I assume the gitlab issue migration needs to happen first.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes