refactor(shorebird_cli): adjust shorebird.yaml flavors format

[felangel]

Description

• refactor(shorebird_cli): adjust shorebird.yaml flavors format (part of fix: Support for multiple Flavors #389)
  • app_id is required
  • flavors is optional

Without Flavors

# This file is used to configure the Shorebird updater used by your application.
# Learn more at https://shorebird.dev
# This file should be checked into version control.

# This is the unique identifier assigned to your app.
# It is used by your app to request the correct patches from Shorebird servers.
app_id: 4baf7a49-0819-4116-bcbb-6d1ed33c154d

With Flavors

# This file is used to configure the Shorebird updater used by your application.
# Learn more at https://shorebird.dev
# This file should be checked into version control.

# This is the unique identifier assigned to your app.
# It is used by your app to request the correct patches from Shorebird servers.
app_id: 4baf7a49-0819-4116-bcbb-6d1ed33c154d
flavors:
  development: 4baf7a49-0819-4116-bcbb-6d1ed33c154d
  production: 872ff0f7-fac5-40da-bd3a-9e46a7d026ab
  staging: 5f5e46b1-d2cb-4a8a-ac1b-97c36a2521e7

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