Synchronize and fix JS/TS linting

[eerikson]

In preparation for some more complicated changes, I wanted to get a handle on our linting situation. We don't currently lint TS or JS right now. In the future, I'd also like to make sure that we lint Markdown.

I've also updated our TypeScript configuration to match the marketing site, another NextJS app.

Both TypeScript and ESLint are just copy-pasted in this change, but next week (or first thing next year) we plan to use the mixpanel-code-config configuration instead (example). I figured this was a good first step.

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:rocket: https://developer.mixpanel.com/v0.0-pr-766/reference/overview Last updated: 12/15/2023, 2:19:21 PM PT from 8ca79d4e8b1a7e13fdcf9fb480442dc291230f8f

[myronkaifung]

Hi @eerikson it doesn't appear that there are any recent commits to this branch. Is this PR good to close?

[tiffanyqi]

Closing for now and will revisit when we get there