reduce number of middleware handlers (#13546)

- combine similar looking functionalities into single
  handlers, and remove unnecessary proxying of the
  requests at handler layer.

- remove bucket forwarding handler as part of default setup
  add it only if bucket federation is enabled.

Improvements observed for 1kiB object reads.
```
-------------------
Operation: GET
Operations: 4538555 -> 4595804
* Average: +1.26% (+0.2 MiB/s) throughput, +1.26% (+190.2) obj/s
* Fastest: +4.67% (+0.7 MiB/s) throughput, +4.67% (+739.8) obj/s
* 50% Median: +1.15% (+0.2 MiB/s) throughput, +1.15% (+173.9) obj/s
```

cmd/healthcheck-handler.go

@@ -28,6 +28,10 @@ import (
 
 const unavailable = "offline"
 
+func shouldProxy() bool {
+	return newObjectLayerFn() == nil
+}
+
 // ClusterCheckHandler returns if the server is ready for requests.
 func ClusterCheckHandler(w http.ResponseWriter, r *http.Request) {
 	if globalIsGateway {