Add a boolean 'enabled' field to the plugin configuration that allows individual plugins to be enabled or disabled.

Requirements

• Add 'enabled' field to plugins/config.yaml with true/false values
• Plugins with enabled: false should not be loaded or executed
• Default behavior should be enabled: true for backward compatibility

Implementation Notes

• Update plugin loading logic to check the enabled field
• Ensure proper validation of the configuration schema
• Consider how this affects existing plugin configurations