[FSSDK-11587] Implement CMAB config

[Mat001]

Added CMAB (Contextual Multi-Armed Bandit) support to Agent

1. CMAB Configuration Integration:
   - Added structured CMABConfig, CMABCacheConfig, and CMABRetryConfig types to config package
   - Implemented JSON-based configuration via OPTIMIZELY_CMAB environment variable
   - Added support for partial configuration via OPTIMIZELY_CMAB_CACHE and OPTIMIZELY_CMAB_RETRYCONFIG
   - Configuration includes request timeouts, cache settings (type, size, TTL), and retry logic with exponential backoff
2. go-sdk Integration:
   - Updated Agent to use go-sdk v2.1.1 with CMAB support
   - Modified defaultLoader() to create go-sdk clients with CMAB service when configured
   - Agent passes CMAB configuration to go-sdk's WithCmabService() factory option
   - Leverages go-sdk's core CMAB service, caching, and decision integration
3. Client Factory Integration:
   - Added CMAB configuration parsing and validation in client creation pipeline
   - Integrated with existing Agent client caching mechanism
4. HTTP Endpoint Enhancement:
   - Enhanced /decide endpoint to return CMAB predictions alongside feature flag decisions
   - No API changes required - CMAB data is included in existing response format when available
   - Agent serves enriched responses from go-sdk's enhanced Decide() method
5. Configuration Refactoring:
   - Refactored from unstructured map[string]interface{} to structured types for better type safety
   - Updated all tests to use structured configuration types
   - Added comprehensive test coverage for various configuration scenarios
6. Documentation & Testing:
   - Updated configuration examples and documentation
   - Added debug logging for troubleshooting CMAB configuration issues

Issues

FSSDK-11587

[jaeopt]

I have a few questions about the config contexts and need your help to catch up.

[jaeopt]

It looks good as is. I'd like to see how we use these configs (cache configs, especially) with go-sdks core.