### Explanation:

- **proxy_mode**: This variable defines the primary configuration mode, such as 'No proxy', 'Auto-detect...', or other options. The default is set to 'No proxy'.

- **proxy_address**: This field specifies the IP address where the proxy will be configured. It has a required type and optional choices.

- **proxy_port**: Specifies the port number for proxy configuration. A default value of 8080 is provided, though it can be adjusted based on user needs.

This schema provides a structured way to handle proxy configurations, allowing users to choose from predefined options with specific settings.