Allow a custom path in Firebase functions custom domain

[segevfiner]

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Fixes #8440

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[changeset-bot]

🦋 Changeset detected

Latest commit: 1eeb535

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@firebase/functions	Patch
firebase	Patch
@firebase/functions-compat	Patch

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[taeold]

Thank you for your contribution!

[dlarocque]

Thanks!

[segevfiner]

Hrmmm. @dlarocque CLA error on your email for some reason...?