Unified Backups: Add support for restoring from a simple backup

Proposal

Following the proposal to support simple backups: #427337 (closed), we should introduce support for restoring from a simple backup.

While we intend to reuse existing code and they may already support advanced workflows, its out of scope to test and make sure they work at this time.

The intended target for this feature is to cover the use-case of 1k reference architecture, file system data only (no object storage support).

Before restoring it should run a pre-check for the following documented prerequisites:

• The destination GitLab instance must have the exact same version

The check should be extracted from existing Rake solution in order to support future extension for Omnibus / Kubernetes use-case.

We should include an option flag (ex: --precheck-only) that only runs the precheck against the provide backup and instance. It should correctly return exit codes when successful and when a failure happens so it can be easily added to scripts.