Add rate limiter for S3 API layer (#9196)

- total number of S3 API calls per server
- maximum wait duration for any S3 API call

This implementation is primarily meant for situations
where HDDs are not capable enough to handle the incoming
workload and there is no way to throttle the client.

This feature allows MinIO server to throttle itself
such that we do not overwhelm the HDDs.

cmd/background-heal-ops.go

@@ -75,7 +75,7 @@ func (h *healRoutine) run(ctx context.Context, objAPI ObjectLayer) {
 			}
 
 			// Wait and proceed if there are active requests
-			waitForLowHTTPReq(int32(globalEndpoints.Nodes()))
+			waitForLowHTTPReq(int32(globalEndpoints.NEndpoints()))
 
 			var res madmin.HealResultItem
 			var err error