Detect empty env vars

[xixixao]

I just burned half an hour thanks to this. Boolean coercion is evil. I was setting these options in CI, and due to a misconfiguration one of them was empty string. What was worse, I couldn't repro this locally, because if you have .env.local with CONVEX_DEPLOYMENT, and even if you're not logged in, npx convex deploy --url "" --admin-key "" does the right thing, but if you don't have .env.local, then you get erronously:

$ npx convex deploy --admin-key "" --url ""
You are currently developing anonymously with a locally running project. To deploy your Convex app to the cloud, log in by running `npx convex login`. See https://docs.convex.dev/production for more information on how Convex cloud works and instructions on how to set up hosting.

I'd turn on a lint rule that disallows boolean coercion altogether (I don't remember why we didn't do it in the past, maybe it didn't exist?).

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[xixixao]

(another one for the != null camp :) )

[thomasballinger]

This is in get-convex/convex-backend@b5718c5, thank you!