allow setting the breakout room limit

mod/html5/settings.yml

@@ -35,7 +35,7 @@ public:
     # Warning: increasing the limit of breakout rooms per meeting
     # can generate excessive overhead to the server. We recommend
     # this value to be kept under 12.
-    breakoutRoomLimit: 8
+    breakoutRoomLimit: {{ .Env.BREAKOUTROOM_LIMIT }}
     defaultSettings:
       application:
         animations: true