Add go/android-hide-passwords-physical-keyboards

[cschlosser]

Description of what this PR is changing or adding, and why: Add a new go link for the hide password on Android design doc.

Issues fixed by this PR (if any): NA

PRs or commits this PR depends on (if any): NA

Presubmit checklist

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  of 80 characters or fewer.

[gemini-code-assist]

Code Review

This pull request adds a new 301 redirect rule in firebase.json for the path /go/android-hide-passwords-physical-keyboards, pointing to a Google Document. I have no feedback to provide.