github action to trigger fastlane build / publish for internal testing

[tomholub]

It would be enough to make a GitHub Action that is manually triggered whenever PR is ready. Let's look into this after the currently opened PR is closed.

Originally posted by @tomholub in #281 (comment)

[Kharchevskyi]

Firstly will try to distribute build with https://firebase.google.com/docs/app-distribution
If this works next step will be to create Fastlane lane for distribution

[Kharchevskyi]

@tomholub which scheme of the app should be distributed?
Debug - com.flowcrypt.ios.debug
Enterprise - com.flowcrypt.ios.enterprise
Release - com.flowcrypt.ios
Testflight - com.flowcrypt.ios.testflight

will test with com.flowcrypt.ios.debug