Warn when configuration uses plugin(s) that require language model but language model is not enabled

[waldekmastykarz]

Feature Proposal

Add a feature to Dev Proxy Toolkit that analyzes the configuration and issues a warning when it detects usage of plugins or plugin configuration that require a language model, but the language model is not enabled in the configuration. This will help prevent misconfigurations where a plugin (or its options) expects a language model but the user has not enabled it, avoiding runtime errors or unexpected failures (such as observed in dotnet/dev-proxy#1314).

Acceptance Criteria

• Use a predefined list of plugins and configurations that require language model
• If any plugin or plugin option requires a language model but it is not enabled in the config, display a clear warning to the user.
• Warning should indicate which plugin(s) or option(s) require the language model.
• Documentation updated to describe this new validation.

Motivation

This feature will help users diagnose configuration problems early, prevent runtime errors, and improve user experience when working with plugins that depend on language model functionality.