This PR has a large blast radius because it takes the final step and bumps up the Controller to be fully async.
We have historically done a piece-by-piece update, so all operations were already async but the controller interface was kept synchronous.
With this update, the controller is now fully async and all tests are updated.
Most places where the new C# compiler warns about function names not ending in `Async` were also adressed, giving a massive refactor change.
Functionally, no changes are done.
This repair will leave the database in a still-broken state, but if this is run prior to purge-broken-files, less data will be lost.
Also updated the purge-broken-files operation to keep files and directories in the set, if they are only missing metadata.
This adds a number of additional features to the repair process so it can actually fully recover if all data is present.
Also added a several tests to ensure that the functionality works in multiple scenarios.
This fixes#5987
Kenneth Skovhede