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/peer-rest-client.go

@@ -614,32 +614,6 @@ func (client *peerRESTClient) BackgroundHealStatus() (madmin.BgHealState, error)
 	return state, err
 }
 
-// BgLifecycleOpsStatus describes the status
-// of the background lifecycle operations
-type BgLifecycleOpsStatus struct {
-	LastActivity time.Time
-}
-
-// BgOpsStatus describes the status of all operations performed
-// in background such as auto-healing and lifecycle.
-// Notice: We need to increase peer REST API version when adding
-// new fields to this struct.
-type BgOpsStatus struct {
-	LifecycleOps BgLifecycleOpsStatus
-}
-
-func (client *peerRESTClient) BackgroundOpsStatus() (BgOpsStatus, error) {
-	respBody, err := client.call(peerRESTMethodBackgroundOpsStatus, nil, nil, -1)
-	if err != nil {
-		return BgOpsStatus{}, err
-	}
-	defer http.DrainBody(respBody)
-
-	state := BgOpsStatus{}
-	err = gob.NewDecoder(respBody).Decode(&state)
-	return state, err
-}
-
 func (client *peerRESTClient) doTrace(traceCh chan interface{}, doneCh chan struct{}, trcAll, trcErr bool) {
 	values := make(url.Values)
 	values.Set(peerRESTTraceAll, strconv.FormatBool(trcAll))