We only allow users that can merge the merge request to push to the
fork.

The query becomes a lot simpler if we can check the branch name as
well instead of having to load all branch names.

When an MR is created using `allow_maintainer_to_push`, we enable some
abilities while the MR is open.

This should allow every user with developer abilities on the target
project, to push to the source project.

Use the max of the `last_activity_at` and `last_repository_updated_at`
columns. The latter is updated only when a push happens, but the former is
updated whenever any activity (e.g. issue creation) happens.

Closes #27181

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix using wildcards in protected tags to expose protected variables

When a project uses fast-forward merging strategy user has
to rebase MRs to target branch before it can be merged.
Now user can do rebase in UI by clicking 'Rebase' button
instead of doing rebase locally.

This feature was already present in EE, this is only backport
of the feature to CE. Couple of changes:
* removed rebase license check
* renamed migration (changed timestamp)

Closes #40301

This reverts merge request !15712

I've followed the [upgrade guide](https://github.com/thoughtbot/factory_bot/blob/4-9-0-stable/UPGRADE_FROM_FACTORY_GIRL.md) and ran these two commands:

```
grep -e FactoryGirl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|FactoryGirl|FactoryBot|"
grep -e factory_girl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|factory_girl|factory_bot|"
```
Signed-off-by: NRémy Coutable <remy@rymai.me>

* new merge request can be created by sending an email to the specific
email address (similar to creating issues by email)
* for the first iteration, source branch must be specified in the mail
subject, other merge request parameters can not be set yet
* user should enable "Receive notifications about your own activity" in
user settings to receive a notification about created merge request

Part of #32878

Note the dependency on gitlab-shell v5.10.0