Refactor logging in more Go idiomatic style (#6816)

This refactor brings a change which allows
targets to be added in a cleaner way and also
audit is now moved out.

This PR also simplifies logger dependency for auditing

cmd/generic-handlers.go

@@ -723,24 +723,25 @@ func (l rateLimit) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	l.handler.ServeHTTP(w, r)
 }
 
-// requestIDHeaderHandler sets x-amz-request-id header.
-// Previously, this value was set right before a response
-// was sent to the client.So, logger and Error response XML
-// were not using this value.
-// This is set here so that this header can be logged as
-// part of the log entry and Error response XML.
-type requestIDHeaderHandler struct {
+// customHeaderHandler sets x-amz-request-id, x-minio-deployment-id header.
+// Previously, this value was set right before a response was sent to
+// the client. So, logger and Error response XML were not using this
+// value. This is set here so that this header can be logged as
+// part of the log entry, Error response XML and auditing.
+type customHeaderHandler struct {
 	handler http.Handler
 }
 
-func addrequestIDHeader(h http.Handler) http.Handler {
-	return requestIDHeaderHandler{handler: h}
+func addCustomHeaders(h http.Handler) http.Handler {
+	return customHeaderHandler{handler: h}
 }
 
-func (s requestIDHeaderHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	// Set unique request ID for each response.
+func (s customHeaderHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Set custom headers such as x-amz-request-id and x-minio-deployment-id
+	// for each request.
 	w.Header().Set(responseRequestIDKey, mustGetRequestID(UTCNow()))
-	s.handler.ServeHTTP(w, r)
+	w.Header().Set(responseDeploymentIDKey, globalDeploymentID)
+	s.handler.ServeHTTP(logger.NewResponseWriter(w), r)
 }
 
 type securityHeaderHandler struct {