feat: Update firebase-functions imports to remove /v2

[google-labs-jules]

This commit updates all Node.js samples in the /Node directory to use the new default firebase-functions imports. All instances of firebase-functions/v2/* have been replaced with firebase-functions/*.

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PR created automatically by Jules for task 18363546177691577298

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[egilmorez]

LGTM! Unless we plan to change the default import back, this seems the way to go.