Implement server notices (#2180)

* Add server_notices config

* Disallow rejecting "server notice" invites

* Update config

* Slightly refactor sendEvent and CreateRoom so it can be reused

* Implement unspecced server notices

* Validate the request

* Set the user api when starting

* Rename function/variables

* Update comments

* Update config

* Set the avatar on account creation

* Update test

* Only create the account when starting
Only add routes if sever notices are enabled

* Use reserver username
Check that we actually got roomData

* Add check for admin account
Enable server notices for CI
Return same values as Synapse

* Add custom error for rejecting server notice invite

* Move building an invite to it's own function, for reusability

* Don't create new rooms, use the existing one (follow Synapse behavior)

Co-authored-by: kegsay <kegan@matrix.org>

roomserver/api/api.go

@@ -3,9 +3,11 @@ package api
 import (
 	"context"
 
+	"github.com/matrix-org/gomatrixserverlib"
+
 	asAPI "github.com/matrix-org/dendrite/appservice/api"
 	fsAPI "github.com/matrix-org/dendrite/federationapi/api"
-	"github.com/matrix-org/gomatrixserverlib"
+	userapi "github.com/matrix-org/dendrite/userapi/api"
 )
 
 // RoomserverInputAPI is used to write events to the room server.
@@ -14,6 +16,7 @@ type RoomserverInternalAPI interface {
 	// interdependencies between the roomserver and other input APIs
 	SetFederationAPI(fsAPI fsAPI.FederationInternalAPI, keyRing *gomatrixserverlib.KeyRing)
 	SetAppserviceAPI(asAPI asAPI.AppServiceQueryAPI)
+	SetUserAPI(userAPI userapi.UserInternalAPI)
 
 	InputRoomEvents(
 		ctx context.Context,