This PR adds a single API endpoint for listing contents of remote source or backend. With this API, we can greatly simplify the FE as it does not need to know about webmodules for each provider, but can just use the single API.
To support this, the fulldisk module was updated slightly to return enumerable meta entries, similar to ms365 and gws providers.
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
Kenneth Skovhede