Add metrics for internal API requests (#2310)

* Add response size and requests total to internal handler

* Move MustRegister calls to New* funcs

* Move MustRegister back to init

* Init at some place, minimize changes

federationapi/routing/routing.go

@@ -29,6 +29,7 @@ import (
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/sirupsen/logrus"
 )
 
@@ -53,6 +54,10 @@ func Setup(
 	servers federationAPI.ServersInRoomProvider,
 	producer *producers.SyncAPIProducer,
 ) {
+	prometheus.MustRegister(
+		pduCountTotal, eduCountTotal,
+	)
+
 	v2keysmux := keyMux.PathPrefix("/v2").Subrouter()
 	v1fedmux := fedMux.PathPrefix("/v1").Subrouter()
 	v2fedmux := fedMux.PathPrefix("/v2").Subrouter()

federationapi/routing/send.go

@@ -74,12 +74,6 @@ var (
 	)
 )
 
-func init() {
-	prometheus.MustRegister(
-		pduCountTotal, eduCountTotal,
-	)
-}
-
 var inFlightTxnsPerOrigin sync.Map // transaction ID -> chan util.JSONResponse
 
 // Send implements /_matrix/federation/v1/send/{txnID}