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/generic-handlers_test.go

@@ -155,7 +155,7 @@ func TestSSETLSHandler(t *testing.T) {
 		r.Header = test.Header
 		r.URL = test.URL
 
-		h := setSSETLSHandler(okHandler)
+		h := setRequestValidityHandler(okHandler)
 		h.ServeHTTP(w, r)
 
 		switch {