docs: initial documentation

[FedericoBiccheddu]

I think this could be a nice addition to this project mostly because:

• There are some nice features coming in the next release
• Could improve library adoption by making easier to work with gqtx without digging into source files and those types for basic usage
• In the future might be needed to have major versions with different behaviour and docs help documenting that

There are some points that need to be discussed before an eventual release:

• Choose the provider for deploying the docs (GitHub Pages? Vercel? Netlify?)
• Maybe use an organization and move the docs in another repo to keep this repo lean?
• What pages are required before publishing the docs

Todo:

• Add custom css to hightlight code lines
• Expand by default every sidebar section

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I created a preview of my branch on Vercel in order to have an idea of the final result: https://gqtx.vercel.app/

[FedericoBiccheddu]

Added Introductions to object types and objectType documentation.

Feedback are much appreciated (mostly my english 😆).

[FedericoBiccheddu]

IMO examples are way to verbose. Docusaurus does not support folding sections for now (see docusaurus/2215) to fold repetitive code but leaving a way to copy the example code.

I'm thinking about an interactive Playground on CodeSandbox to solve this problem, but I don't know if it is better to create a sandbox for each example or a fully functional project with every gqtx feature.

What are your thoughts? Maybe is better to track this in another issue to gather feedbacks?