Add /_dendrite/admin/purgeRoom/{roomID} (#2662)

This adds a new admin endpoint `/_dendrite/admin/purgeRoom/{roomID}`. It
completely erases all database entries for a given room ID.

The roomserver will start by clearing all data for that room and then
will generate an output event to notify downstream components (i.e. the
sync API and federation API) to do the same.

It does not currently clear media and it is currently not implemented
for SQLite since it relies on SQL array operations right now.

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>
Co-authored-by: Till Faelligen <2353100+S7evinK@users.noreply.github.com>

roomserver/storage/shared/storage.go

@@ -43,6 +43,7 @@ type Database struct {
 	MembershipTable     tables.Membership
 	PublishedTable      tables.Published
 	RedactionsTable     tables.Redactions
+	Purge               tables.Purge
 	GetRoomUpdaterFn    func(ctx context.Context, roomInfo *types.RoomInfo) (*RoomUpdater, error)
 }
 
@@ -1445,6 +1446,21 @@ func (d *Database) ForgetRoom(ctx context.Context, userID, roomID string, forget
 	})
 }
 
+// PurgeRoom removes all information about a given room from the roomserver.
+// For large rooms this operation may take a considerable amount of time.
+func (d *Database) PurgeRoom(ctx context.Context, roomID string) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		roomNID, err := d.RoomsTable.SelectRoomNIDForUpdate(ctx, txn, roomID)
+		if err != nil {
+			if err == sql.ErrNoRows {
+				return fmt.Errorf("room %s does not exist", roomID)
+			}
+			return fmt.Errorf("failed to lock the room: %w", err)
+		}
+		return d.Purge.PurgeRoom(ctx, txn, roomNID, roomID)
+	})
+}
+
 func (d *Database) UpgradeRoom(ctx context.Context, oldRoomID, newRoomID, eventSender string) error {
 
 	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {