Project: use clone URL from connected repository if available (#11826)
- If the user selects a remote repository, the repo field is hidden, if
the user doesn't select a remote repo, they can edit the field.
- We always try to use the clone url from the remote repo if available
- When importing a project, the repo field is shown as read-only (except
on manual import of course).
We have close to 7K projects with a remote repo attached with a
different clone URL on .org, and 700 on .com.
```
In [4]: Project.objects.filter(remote_repository__isnull=False).filter(~Q(repo=F('remote_repository__clone_url'))).count()
Out[4]: 6869
In [1]: Project.objects.filter(remote_repository__isnull=False).filter(~Q(repo=F('remote_repository__clone_url'))).count()
Out[1]: 739
```
Do we care? Should I analyze those further? Should we contact users?
Closes https://github.com/readthedocs/readthedocs-corporate/issues/1859