This PR adds a flag to the test method so we can choose to test for read-only access (needed for restore) or read-write (needed for backups).
Additionally, this PR fixes a logic bug in that the BackendSourceProvider would not actually test the connection, but just check the placeholder element returned (which is always returned). With this PR the backend's ListAsync command is tested fully.
Also renamed the methods on ISourceProvider to have the `...Async` prefix.
This replaces #6939
Instead of requesting all scopes up front, each sub-section of the backup/restore will request the permissions that are relevant for the operation.
The effect is that it is not required to grant all permissions to get a backup running. If permissions are failing, that part of the backup will generate warnings for items that are excluded.
Kenneth Skovhede