Extension Framework Documentation Updates

[wbreza]

Extension Framework Documentation Enhancement

This PR adds comprehensive missing service documentation and examples to extension-framework.md based on proto file analysis.

Key Additions:

New gRPC Service Documentation:

• Container Service - container management operations
• Framework Service - custom language/framework provider registration
• Service Target Service - custom deployment target providers
• Extension Service - extension lifecycle management

Enhanced Existing Services:

• Event Service - added ServiceContext artifact management documentation
• Account/Prompt Services - enhanced with complete method documentation and examples

Extension Development Improvements:

• Complete ExtensionHost builder pattern example from Demo extension
• Comprehensive extension manifest schema documentation covering all properties
• Added new capabilities: mcp-server, service-target-provider, framework-service-provider
• Dependencies, providers, MCP configuration, and platform-specific metadata documentation

Structure Updates:

• Updated Table of Contents for all new services
• Added practical Go code examples throughout
• Complete extension manifest examples with full schema coverage