fix: various optimizations, idiomatic changes (#9179)

- acquire since leader lock for all background operations
  - healing, crawling and applying lifecycle policies.

- simplify lifecyle to avoid network calls, which was a
  bug in implementation - we should hold a leader and
  do everything from there, we have access to entire
  name space.

- make listing, walking not interfere by slowing itself
  down like the crawler.

- effectively use global context everywhere to ensure
  proper shutdown, in cache, lifecycle, healing

- don't read `format.json` for prometheus metrics in
  StorageInfo() call.

cmd/xl-sets.go

@@ -392,6 +392,11 @@ func (s *xlSets) StorageInfo(ctx context.Context, local bool) StorageInfo {
 		storageInfo.Backend.Sets[i] = make([]madmin.DriveInfo, s.drivesPerSet)
 	}
 
+	if local {
+		// if local is true, we don't need to read format.json
+		return storageInfo
+	}
+
 	storageDisks, dErrs := initStorageDisksWithErrors(s.endpoints)
 	defer closeStorageDisks(storageDisks)