Refactor how things are migrated

src/block/repair.rs

@@ -178,6 +178,7 @@ struct ScrubWorkerPersisted {
 	time_last_complete_scrub: u64,
 	corruptions_detected: u64,
 }
+impl garage_util::migrate::InitialFormat for ScrubWorkerPersisted {}
 
 enum ScrubWorkerState {
 	Running(BlockStoreIterator),

src/block/resync.rs

@@ -63,6 +63,7 @@ struct ResyncPersistedConfig {
 	n_workers: usize,
 	tranquility: u32,
 }
+impl garage_util::migrate::InitialFormat for ResyncPersistedConfig {}
 
 enum ResyncIterResult {
 	BusyDidSomething,