Initial Store & Forward Implementation (#2917)

This adds store & forward relays into dendrite for p2p.
A few things have changed:
- new relay api serves new http endpoints for s&f federation
- updated outbound federation queueing which will attempt to forward
using s&f if appropriate
- database entries to track s&f relays for other nodes

setup/base/base.go

@@ -595,6 +595,12 @@ func (b *BaseDendrite) WaitForShutdown() {
 			logrus.Warnf("failed to flush all Sentry events!")
 		}
 	}
+	if b.Fulltext != nil {
+		err := b.Fulltext.Close()
+		if err != nil {
+			logrus.Warnf("failed to close full text search!")
+		}
+	}
 
 	logrus.Warnf("Dendrite is exiting now")
 }