Load Firebase Config in CodeMagic with Environment Variables

[pookzzz]

Ensure the build runs out correctly in Codemagic and able to download from Testmagic.

Reference
https://medium.com/flutter-community/how-to-load-firebase-config-in-codemagic-with-environment-variables-e36e0378b7e6
https://drive.google.com/file/d/1RO_iYctyINxcscHwRc3f4GWEWaT2lUyJ/view
encode-config-files.txt