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

packages/types/src/definitions/runtime/RuntimeStore.type.ts

@@ -22,4 +22,7 @@ export type RuntimeStore = {
 
   // extra timers
   auxtimer1: SimpleTimerState;
+
+  // flags
+  frozen: boolean;
 };