MSC2836: Threading - part one (#1589)

* Add mscs/hooks package, begin work for msc2836

* Flesh out hooks and add SQL schema

* Begin implementing core msc2836 logic

* Add test harness

* Linting

* Implement visibility checks; stub out APIs for tests

* Flesh out testing

* Flesh out walkThread a bit

* Persist the origin_server_ts as well

* Edges table instead of relationships

* Add nodes table for event metadata

* LEFT JOIN to extract origin_server_ts for children

* Add graph walking structs

* Implement walking algorithm

* Add more graph walking tests

* Add auto_join for local rooms

* Fix create table syntax on postgres

* Add relationship_room_id|servers to the unsigned section of events

* Persist the parent room_id/servers in edge metadata

Other events cannot assert the true room_id/servers for the
parent event, only make claims to them, hence why this is
edge metadata.

* guts to pass through room_id/servers

* Refactor msc2836 to allow handling from federation

* Add JoinedVia to PerformJoin responses

* Fix tests; review comments

cmd/dendrite-monolith-server/main.go

@@ -23,6 +23,7 @@ import (
 	"github.com/matrix-org/dendrite/eduserver/cache"
 	"github.com/matrix-org/dendrite/federationsender"
 	"github.com/matrix-org/dendrite/internal/config"
+	"github.com/matrix-org/dendrite/internal/mscs"
 	"github.com/matrix-org/dendrite/internal/setup"
 	"github.com/matrix-org/dendrite/keyserver"
 	"github.com/matrix-org/dendrite/roomserver"
@@ -148,6 +149,12 @@ func main() {
 		base.PublicMediaAPIMux,
 	)
 
+	if len(base.Cfg.MSCs.MSCs) > 0 {
+		if err := mscs.Enable(base, &monolith); err != nil {
+			logrus.WithError(err).Fatalf("Failed to enable MSCs")
+		}
+	}
+
 	// Expose the matrix APIs directly rather than putting them under a /api path.
 	go func() {
 		base.SetupAndServeHTTP(