Add Toolpad file schema reference to the docs

[Janpot]

Generates documentation that describes the Toolpad configuration files

See https://deploy-preview-1940--mui-toolpad-docs.netlify.app/toolpad/schema-reference/

[mnajdova]

For the types that are described below, like NameStringValuePair, would it be feasable to show them in a tooltip when hovering? It will help with not having to scroll back and forth.

Looks much better than the first iteration.

[mnajdova]

Not related to this PR: This can probably be better typed.

[Janpot]

It has

                   "enum": [
                      "query",
                      "mutation"
                    ],

I'll improve this in the docs like:

[Janpot]

@mnajdova Added a tooltip.

Screen.Recording.2023-05-08.at.12.53.08.mov