Allow idiomatic usage of middlewares in gorilla/mux (#9802)

Historically due to lack of support for middlewares
we ended up writing wrapped handlers for all
middlewares on top of the gorilla/mux, this causes
multiple issues when we want to let's say

- Overload r.Body with some custom implementation
  to track the incoming Reads()
- Add other sort of top level checks to avoid
  DDOSing the server with large incoming HTTP
  bodies.

Since 1.7.x release gorilla/mux provides proper
use of middlewares, which are honored by the muxer
directly. This makes sure that Go can honor its
own internal ServeHTTP(w, r) implementation where
Go net/http can wrap into its own customer readers.

This PR as a side-affect fixes rare issues of client
hangs which were reported in the wild but never really
understood or fixed in our codebase.

Fixes #9759
Fixes #7266
Fixes #6540
Fixes #5455
Fixes #5150

Refer https://github.com/boto/botocore/pull/1328 for
one variation of the same issue in #9759

cmd/gateway-main.go

@@ -203,13 +203,16 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 	// Add API router.
 	registerAPIRouter(router, encryptionEnabled, allowSSEKMS)
 
+	// Use all the middlewares
+	router.Use(registerMiddlewares)
+
 	var getCert certs.GetCertificateFunc
 	if globalTLSCerts != nil {
 		getCert = globalTLSCerts.GetCertificate
 	}
 
 	httpServer := xhttp.NewServer([]string{globalCLIContext.Addr},
-		criticalErrorHandler{registerHandlers(router, globalHandlers...)}, getCert)
+		criticalErrorHandler{router}, getCert)
 	httpServer.BaseContext = func(listener net.Listener) context.Context {
 		return GlobalContext
 	}