Added documentation for Firebase Auth Setup

[AgentBurgundy]

I noticed others (including myself long ago) asking questions on how to handle firebase auth. I figured the docs could use an update as it would save a lot of headache answering the same question over and over. Please feel free to edit if anything style wise or content wise is off or not following a standard.

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Name	Status	Preview	Comments	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 10, 2023 2:26am

[louisgv]

@AgentBurgundy thank you for the PR - might need to move the path to align with our current sidebar. Will review shortly