[META] Automate restoring a database with Wal-E

• Automate creating a database host with terraform and applying a role. (https://gitlab.com/gitlab-com/infrastructure/issues/1719)
• Write a cookbook that we can apply to a newly created host using chef-solo that sets it up. (https://gitlab.com/gitlab-com/infrastructure/issues/1720)
• Make sure that it actually restores the database to the point where it's needed.

cc/ @gl-infra