feat: add macOS platform support

[mxknt]

Description

This PR adds macOS as a supported platform, including the required XCode build configurations and run schemes to support the usual three Flutter flavors: production, staging and development. See VeryGoodOpenSource/very_good_cli#452

The process of adding macOS support took the following steps (roughly mapped to the included commits):

• add the basic macOS project scaffold using flutter create --platforms=macos ., removing the new main.dart and other unneeded files that the command added.
• add the required xcode build configurations for each flavor, Debug-development, Release-staging etc.
• update the bundle id for the development and staging build configurations, adding a .dev and .stg suffix respectively.
• add icon assets for each flavor
• add xcode run schemes for each flavor

Type of Change

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