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

federationapi/storage/postgres/storage.go

@@ -62,6 +62,14 @@ func NewDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions,
 	if err != nil {
 		return nil, err
 	}
+	assumedOffline, err := NewPostgresAssumedOfflineTable(d.db)
+	if err != nil {
+		return nil, err
+	}
+	relayServers, err := NewPostgresRelayServersTable(d.db)
+	if err != nil {
+		return nil, err
+	}
 	inboundPeeks, err := NewPostgresInboundPeeksTable(d.db)
 	if err != nil {
 		return nil, err
@@ -104,6 +112,8 @@ func NewDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions,
 		FederationQueueEDUs:      queueEDUs,
 		FederationQueueJSON:      queueJSON,
 		FederationBlacklist:      blacklist,
+		FederationAssumedOffline: assumedOffline,
+		FederationRelayServers:   relayServers,
 		FederationInboundPeeks:   inboundPeeks,
 		FederationOutboundPeeks:  outboundPeeks,
 		NotaryServerKeysJSON:     notaryJSON,