feat(dashboard): add DatadogDashboard v1alpha2 CRD with native YAML widgets

[starlightromero]

Summary

Implements DatadogDashboard v1alpha2 CRD with native YAML widgets, replacing JSON string format with structured YAML arrays for improved developer experience.

Changes

• ✅ New v1alpha2 API: Added DashboardWidget and WidgetLayout structs with native YAML support
• ✅ Enhanced Validation: Comprehensive validation with detailed error messages for all widget types
• ✅ Version-aware Controller: Updated controller to handle both v1alpha1 and v1alpha2 seamlessly
• ✅ Backward Compatibility: Existing v1alpha1 dashboards continue to work unchanged
• ✅ Comprehensive Testing: 51+ test cases including property-based tests for correctness
• ✅ Updated Documentation: Migration guide and examples showing YAML array benefits
• ✅ CRD Generation: Proper OpenAPI v3 schema with v1alpha2 as storage version

Benefits

• 🎯 Native YAML syntax - No more JSON strings, pure Kubernetes YAML
• 🔧 Better IDE support - Auto-completion and validation in editors
• 🛡️ Type safety - Compile-time validation of widget structure
• 📚 Enhanced DX - Cleaner, more readable dashboard definitions

Testing

• All existing tests pass (100% backward compatibility)
• 8 property-based tests validate correctness properties
• Integration tests ensure both API versions coexist
• Comprehensive validation tests for all 27 widget types

Migration

Users can migrate from v1alpha1 to v1alpha2 by:

1. Changing apiVersion to datadoghq.com/v1alpha2
2. Converting JSON string widgets to YAML arrays
3. Optionally adding layout information to widgets

Closes

Fixes #2423

Example

Before (v1alpha1):

spec:
  widgets: '[{"definition": {"type": "timeseries", "title": "CPU"}}]'

After (v1alpha2):

spec:
  widgets:
    - definition:
        type: timeseries
        title: CPU Usage
      layout:
        x: 0
        y: 0
        width: 4
        height: 2

[starlightromero]

@rtrieu Thanks for the approval. Any chance you can provide an ETA on when this can be merged in?

[rtrieu]

hi @starlightromero my approval was from an editorial perspective. this update as a whole will need to be reviewed and approved by a different team (Container Ecosystems) before merging.

[starlightromero]

@rtrieu thank you providing insight into the process. What is the estimated timeline for review by the Container Ecosystems team?