Do script for packaging and updating allowed_addons.json for Fenix
For fenix#40062 (closed) we shipped a default
allowed_addons.json containing a list of allowed addons fetched from mozilla. We should create a script for keeping this list up-to-date and replace the default one from Fenix. We could also check that the https-everywhere and noscript versions in this file are consistent with the ones we ship.