Documentation for the new DX

[kiwicopple]

What kind of change does this PR introduce?

Updates the docs with the new developer experience: https://deploy-preview-253--supabase.netlify.app/docs

• Documents the new Auth using gotrue-js

• Fixes docs: Subscriptions - add instructions for listening to row level changes #179

• Add OAuth links Add Auth/User Management to homepage #241 (comment)

• Add docs on Policies

Additional context

Related PR on supabase-js supabase/supabase-js#50

[kiwicopple]

I've moved over the REST calls to the new response format, and in the process I decided to remove the "import" snippets from all the code examples. It think it makes the docs easier to read and focuses the Developer on the specific piece of code they will be using

Change on the left, original on the right.

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