Add merge request refs to origin
When a drupal.org project gets prepared for dorgflow, we should also add the refs for merge requests:
```
git config --add remote.origin.fetch "+refs/merge-requests/*/head:refs/remotes/origin/merge-requests/*"
git fetch origin
```
But only if that is not yet present, find out with `git config --get-all remote.origin.fetch`
issue