Stop supporting Google Cloud and Azure as backup strategies

What does this MR do?

It removes support for Azure and Google Cloud as backup strategies (via Fog).

Motivation behind this decision can be found in !4928 (closed), !6713 (closed) but basically they require a lot of gems that are unrelated to the backup use-case.

Are there points in the code the reviewer needs to double check?

Am I missing any other location where we'd use these gems?

/cc @rspeicher

Shall we announce that before? What about people that rely on that backup strategies? Should we give them time to move to a different provider?

These strategies are actually currently broken, so... :/ But yeah I agree that it'd be nice to document alternative methods in our documentation.

Status changed to merged

Mentioned in commit e2f66373

This created big issues on our company.

We did not realize that Gitlab stopped backing up to google cloud.
We had to restore last backup because of a disk failure, but now we lost a week of work, because it was not backup up to google cloud.

You have to warn users about this before removing such important feature.

Now please document it about how to manually add Google backup feature again.

mentioned in issue #26362 (closed)