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/gateway-main.go

@@ -267,7 +267,7 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 	if globalCacheConfig.Enabled {
 		// initialize the new disk cache objects.
 		var cacheAPI CacheObjectLayer
-		cacheAPI, err = newServerCacheObjects(context.Background(), globalCacheConfig)
+		cacheAPI, err = newServerCacheObjects(GlobalContext, globalCacheConfig)
 		logger.FatalIf(err, "Unable to initialize disk caching")
 
 		globalObjLayerMutex.Lock()
@@ -277,7 +277,7 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 
 	// Populate existing buckets to the etcd backend
 	if globalDNSConfig != nil {
-		buckets, err := newObject.ListBuckets(context.Background())
+		buckets, err := newObject.ListBuckets(GlobalContext)
 		if err != nil {
 			logger.Fatal(err, "Unable to list buckets")
 		}