fix: Add dotenv support for localhost

[ianvieira]

Adds the dotenv package to create the same support for localhost running and for glitch, making the support consistent between both.

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[ianvieira]

Signed CLA

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[petele]

Hi - thanks for the PR! I've been trying to keep the codelab simple, with as few requirements as possible. Adding dotenv looks pretty low cost, but for now, I'm going to not add it. Developers can easily update the server.js if they want to experiment from their own computer.