feat: Support external-secrets v1

[kosuke-fujishiro]

Add support for external-secrets v1 API alongside existing v1beta1 support

Changes

• ✨ New ExternalSecretV1 class with external-secrets.io/v1 API version
• 🔄 Enhanced schema supporting v1 features:
  • New SourceRef interface allowing store or generator references
  • Optional secretStoreRef in spec (can be specified per data item)
  • Added refreshPolicy option (CreatedOnce, Periodic, OnChange)
  • Optional remoteRef in data (when using sourceRef)
• 🎯 Default export now uses v1 (ExternalSecret = ExternalSecretV1)
• ✅ Comprehensive tests for v1, v1beta1, and default behavior
• 📚 Updated API documentation with v1 interfaces
• 🔒 Backward compatibility maintained for v1beta1 users

This update aligns with the external-secrets operator's stable v1 release, providing more flexible configuration options while maintaining full backward compatibility for existing v1beta1 implementations.