feat: log coverage when is a valid build

[jamesblasco]

Description

Adds log message displaying coverage when this is above the min coverage.

If coverage is 100% it will be displayed like:

    Coverage: 100%.

If coverage is below 100% but still above min_coverage, it will be displayed as:

    Coverage: 95%.
    Coverage is more than min_coverage 80.
    
    Lines not covered:
      - /Users/felix/Development/github.com/felangel/bloc/packages/bloc/lib/src/bloc_observer.dart: 20, 27, 36, 43, 51

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