Platform API guide

[stopachka]

Demo: https://instant-www-js-papi-jsv.vercel.app/docs/platform-api

This PR adds a guide for our platform features.

We cover:

1. The tools to use (CLI + Platform SDK)
2. How to create temporary apps
3. How to create long-lived app
4. How to change schema and perms

More changes:

• I moved the platform ouath guide out of the navigation. I was originally going to link it inside this doc, but I realize the Oauth guide in our Github links it, and it seems to flow more naturally there. So linked to the Oauth guide instead
• I fixed the platform token window, as it scrolled
• I made it so the CLI --token works with personal / platform access tokens
• Changed the category title "Platform Features" to "Instant Features"

@dwwoelfel @nezaj @drew-harris

[github-actions]

View Vercel preview at instant-www-js-papi-jsv.vercel.app.

[dwwoelfel]

It might be nice to show how you can create a temporary app with schema and permissions using the platform sdk.

[stopachka]

Good idea!