Rename groupcall.txt -> groupcall.json.

This will stop groupcall.txt being handled as a 'log file' and instead
indicate it's an artifact to be stored alongside the rageshake.

The file will still be stored on the rageshake server but the extension
will indicate it's not a log file.

src/settings/rageshake.js

@@ -189,7 +189,7 @@ export function useSubmitRageshake() {
             body.append(
               "file",
               new Blob([JSON.stringify(json)], { type: "text/plain" }),
-              "groupcall.txt"
+              "groupcall.json"
             );
           }
         }