Improve user file restoration process

[sffc]

Currently, user file restoration requires manual intervention from the site admin. The site admin manually searches for the gs:// URI of the user file backup and then restores the account from that path.

This process could be improved by taking the following steps, which can be done independently:

• Automatically find the gs:// URIs for a given account, and expose it in the admin panel. Caveat: The GCP API for searching within the Cloud Storage bucket is quite slow; we may want to consider caching the URIs in a database or cache for faster lookup.
• Allow users to access the URIs and perform the restoration themselves.