add freeze feature to rundown (#1106)

* add frozen flag to runtime store

* add middleware for when frozen

* prevent rundown editing when frozen

* add endpoint to router to set frozen state

* add frozen property to rundown placeholder in client

apps/server/src/app.ts

@@ -188,6 +188,7 @@ export const startServer = async (
       playback: SimplePlayback.Stop,
       direction: SimpleDirection.CountDown,
     },
+    frozen: false,
   });
 
   // initialise logging service, escalateErrorFn is only exists in electron