fix: `GoogleService-Info.plist` file not found by Firebase SDK unless added to target

[russellwheatley]

Description

I noticed whilst debugging this issue that initialization was occurring from the dart config file, not the GoogleService-Info.plist file. It appears Firebase will not pick up the file unless it is added to the target.

I also think we should stop writing the config to the DefaultFirebaseOptions class for android & iOS. Unnecessary and, I think, confusing to users.

Type of Change

• [ ] ✨ feat -- New feature (non-breaking change which adds functionality)
• [X] 🛠️ fix -- Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ ! -- Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 refactor -- Code refactor
• [ ] ✅ ci -- Build configuration change
• [ ] 📝 docs -- Documentation
• [ ] 🗑️ chore -- Chore

[russellwheatley]

@Salakar I've updated to abort() ruby script (exit code 1 and writes to stderr), if no "Runner" target exists, then throw exception in CLI to let the user know the issue.

Example:

[salahamassi]

I tried to fix this here https://github.com/invertase/flutterfire_cli/pull/88