Graceful shutdowns (#1734)

* Initial graceful stop

* Fix dendritejs

* Use process context for outbound federation requests in destination queues

* Reduce logging

* Fix log level

cmd/dendrite-monolith-server/main.go

@@ -144,6 +144,7 @@ func main() {
 		KeyAPI:              keyAPI,
 	}
 	monolith.AddAllPublicRoutes(
+		base.ProcessContext,
 		base.PublicClientAPIMux,
 		base.PublicFederationAPIMux,
 		base.PublicKeyAPIMux,
@@ -176,5 +177,5 @@ func main() {
 	}
 
 	// We want to block forever to let the HTTP and HTTPS handler serve the APIs
-	select {}
+	base.WaitForShutdown()
 }