Enable optional grpc reflection

[rothgar]

Feature Request

I would like a kernel flag that can enable grpc api reflection for exploring the Talos API and making it easier to build tools that use the API.

Description

When learning the API it would be helpful to have an OpenAPI-like spec that would help me understand the methods and how to use them. This would also help with creating custom tools to consume/use the API.

To get started I would like to use tools like grpcurl and grpcui to be able to show how the API works and what methods are available for a running system (not just docs and code).

This should be enabled with an optional kernel argument and off by default because it can be considered a security risk.