This is for compaction part of ENG-7012. We might want to resume existing compaction when it was created but hasn't been uploaded.
Original compaction promise resumes after successful upload, so added a callback that is triggered after compaction is created but before it's uploaded.
To avoid significant changes to RustPromiseManager, on C++ side, I had to create a dummy Promise that calls the callback when resolved.

Depends on D14886

Triggered backup from backup menu. Confirmed that console log from the callback has the same backupID that is later resolved when the upload promise fulfills.