Feature Request: Support offsite-backups and restoring customers

[envoyr]

Describe the solution you would like to see
It should be possible for admins & resellers to create offsite backups for customers. It is planned that customer data, web space, databases and email accounts can be backed up to an external server.

Additional context
Accordingly, it should be possible to completely backup customers and then back them up to external servers, in case of emergency, a complete restore should be possible.

This feature could also be used to move customers to another froxlor server more easily.

Planned interfaces for transfer are: S3, SFTP, FTPS, Local

Note
This will be a post-release feature for 2.x

[JB1985]

Webdav would be great to use (for example) nextcloud.

[realrellek]

I think some of the "infrastructure" could be useful for the clean-migration as well (ref #1232)

So there could be an export with all the customers (assigned to their admins/resellers) and all the password hashes (for databases: playing by the same rules as the migration)

That way, you could also restore a backup from the SQL dumps and the htdocs, you know, in case of emergency.

(I know about the discussion that it may or may not be pushed even further because there are good backup solutions that froxlor will never be able to compete with... I am just writing down my thoughts on how we could re-use some of the code for another feature. So that whatever gets implemented first also thinks of the other and, well, gets designed in a way that it usable for a greater scheme)