Support serverless Function datasource

[Janpot]

First iteration on #628.

• Write arbitrary code that gets executed on the server, the result is made available as state on the page
• Implements a subset of the fetch API
• Pass parameters from the page
• Define secrets that can be used in the code
• Debug with console.log + request logging

Screen.Recording.2022-07-07.at.17.58.03.mov

• We should rethink the UX around secrets/credentials

Closes #628

[render]

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[apedroferreira]

pretty cool!
i was thinking something more like being able to set custom functions for any type of custom server-side code / API call, and the "query" option could probably just take a URL and make only GET requests - but i'm sure you've tried different approaches and seen what's best
anyway this looks great, i had never heard of this library but running an isolated process like that seems great

[render]

Your Render PR Server URL is https://toolpad-pr-641.onrender.com.

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