Enable back up for Azure file share

[thekaveman]

With #1773 we mount an Azure File Share to store the Sqlite database file and persist between app restarts.

As we continue building out the Admin interface, and especially once it is in "live" usage, we'll want to ensure our database file is backed up on some schedule, in case we ever need to recover.

Acceptance Criteria

• The terraform definition of the Azure File Share enables back ups
• Back up schedule is at least once per day, preferably in the evening (> 6pm Pacific)
• Retention schedule is at least one week

Additional context

Azure docs: Back up Azure file shares