feat: Add dynamic client configuration support

[ByeongUkChoi]

Summary

This PR adds support for server-side dynamic client configuration in LiveKit Server, enabling administrators to configure client behavior based on client characteristics (browser, OS, device model, etc.) without requiring client-side code changes.

Background

Previously, LiveKit Server only supported static client configurations that were hardcoded in the StaticConfigurations variable. This made it difficult to:

• Respond to new device issues - Required server code changes and releases
• Test configurations - No way to A/B test different configurations
• Environment-specific configs - Same configurations across all environments
• Runtime adjustments - Required server restarts for any changes

Changes

New Features

• YAML Configuration Support: Configure client rules in config.yaml
• Runtime Updates: Update configurations without server restart
• Rule-based Matching: Use JavaScript-like expressions to match clients
• Merge Strategy: Choose to merge with or override static configurations
• Backward Compatible: Existing static configurations continue to work

Files Added

• pkg/clientconfiguration/dynamicconfiguration.go - Dynamic configuration manager
• pkg/clientconfiguration/dynamicconfiguration_test.go - Unit tests
• pkg/service/clientconfigurationservice.go - API service for future use
• examples/dynamic_config_example.go - Example usage

Files Modified

• pkg/config/config.go - Added ClientConfigurationConfig and ClientConfigurationItem structs
• pkg/service/roommanager.go - Integration with DynamicClientConfigurationManager
• config-sample.yaml - Added configuration examples

Configuration Example

client_configuration:
  configurations:
    # Disable AV1 for older Safari versions
    - match: 'c.browser == "safari" && c.browser_version < "17.0"'
      configuration: '{"disabled_codecs": {"codecs": [{"mime": "video/AV1"}]}}'
      merge: true
    
    # Enable hardware encoder for Android
    - match: 'c.os == "android"'
      configuration: '{"video": {"hardware_encoder": 1}}'
      merge: true

Match Rule Expressions

Support JavaScript-like expressions with client fields:

• c.browser - Browser name (safari, chrome, firefox)
• c.browser_version - Browser version string
• c.os - Operating system (android, ios, windows, etc.)
• c.device_model - Device model string
• c.sdk - SDK name
• c.protocol - Protocol version

Implementation Details

Architecture

1. DynamicClientConfigurationManager extends the existing ClientConfigurationManager interface
2. Fallback Strategy - Falls back to static configuration if dynamic initialization fails
3. Configuration Merging - Dynamic configs can be merged with static ones using protobuf merge
4. Thread-Safe - Uses RWMutex for concurrent access during updates

Backward Compatibility

• Zero breaking changes
• Existing static configurations work unchanged
• Servers without dynamic configuration behave exactly as before
• Dynamic configurations supplement static ones by default