Setup .env check before building the app

Anything we add in the .env file will end up being bundled into the final release APK. While extracting an APK to get it's content, I have seen some variables in the .env file that we don't use in the project, probably added temporarily to it in the machine that built the release APK, which then didn't get removed

We need to either add this check to this repo itself or to mobile-operator