add support for bucket level request count per API (#17468)

New metrics added to calculate API request count
per bucket, per API.  Captures errors, including
4xx, 5xx HTTP status codes separately.

cmd/globals.go

@@ -245,8 +245,9 @@ var (
 	// Global HTTP request statisitics
 	globalHTTPStats = newHTTPStats()
 
-	// Global bucket network statistics
+	// Global bucket network and API statistics
 	globalBucketConnStats = newBucketConnStats()
+	globalBucketHTTPStats = newBucketHTTPStats()
 
 	// Time when the server is started
 	globalBootTime = UTCNow()