Adds some settings to check flipper-server state

Summary:
There's one setting: to enable or disable flipper-server.

However, I've added some current running state to it. If there's a better way of doing this, please do let me know.

Reviewed By: aigoncharov

Differential Revision: D37276670

fbshipit-source-id: f6c941cf0cfe55c267b9bcb9f799934fba1e28ef

desktop/flipper-common/src/settings.tsx

@@ -58,6 +58,9 @@ export type Settings = {
     host?: string;
     port?: number;
   };
+  server?: {
+    enabled: boolean;
+  };
 };
 
 export enum ReleaseChannel {