Create and mount custom persistent Azure file share

[thekaveman]

This is a follow up to #1763

Now we can customize the location that Django creates and looks for its Sqlite database file 👍 But we can't write to a persistent storage location, because our app service container overwrites the Azure-provided persistent file system each restart.

But we can create and mount a custom persistent file share in Azure, and maybe that works as a way to keep the Sqlite database.

Acceptance Criteria

• Terraform creates and mounts an Azure File Share into app container directory
• App config django-db-dir points to mounted share

Additional context

Azure docs: Mount Azure Storage as a local share in App Service

Potential alternative to #1774

[thekaveman]

This appears to be working for now! Pending some more testing and activation of the admin interface.