Allow other backup centers

From https://gitlab.com/gitlab-com/githost/issues/65#note_27051317

We are getting more and more requests from potential GitHost customers to provide a backup location within the EU due to data security/privacy concerns. It diminishes the benefits of a hosting location in Europe if the backup data is stored somewhere else.

A large prospect would like to buy a yearly corporate plan + EE but can't if we store backups outside of Europe. https://na34.salesforce.com/0016100000NmTVx /cc @ernstvn

@dblessing Would "Backup uploading to custom S3" allow customers to use their own backup location in S3?

\cc @jameslopez

mentioned in issue #65 (closed)

Allowing customers to use their own backup locations would be good. Providing additional backup locations as part of our service offering is equally good given the comments from @teemo above. We tell people they can host in any of DO's data centers. That should also include allowing at least some selection of backup location data center.

There is a list here of S3 data centres, including three in Europe: http://docs.aws.amazon.com/AmazonS3/latest/dev/Introduction.html

A company (based in Germany) confirmed this morning that they would have to cancel their GitHost subscription and move to self-hosted because we couldn't guarantee backup location in the EU. Not a big prospect (20 EES currently), but a data point for the discussion.

@simonwill I scrubbed the name of the company from your comment, since this issue is public (to the world).

mentioned in merge request www-gitlab-com!7307 (closed)