Add support for prompts (built-in and custom)

[julia-yin]

Add support for prompts (both built-in and user-customizable) which provide LLM instructions on how to use the tools for specific scenarios. For example, one prompt can cover networking checks which will deploy debug pods / gadgets and check for any network failures. Users can also contribute their own prompts based on specific use cases for their clusters.

Compile a list of prompts + investigate which agents support prompts currently