Documenting Custom Agent

[valentimarco]

At the moment, the docs doesn't provide a guide to build custom Agent with the new structure introduced on 1.7.X.

I was thinking about this:

1. Show how you can create your custom flow with this new tool (Even better to introduce a diagram that explain what are you doing step by step)
2. How can you integrate custom logic or libraries like HayStack, LLamaIndex, GraphRag, GuardRails, NVIDIA NeMo Guardrails
   (Yes, can be a blog post but adding simple ref to this popolar libraries can help. Particularly for guardrails libraries!)
3. Explain difference between OpenAi AssistanceAPI (even if...)

All of this should be written in a markdown file under mkdocs/framework/cat-components/cheshire_cat/agent/custom_agent.md

[pieroit]

I'd like to refine more the API of those python classes, are you already using it?

Point 2 really cool