Update Firebase Function to Node 20

[Mephistic]

Summary
The version of Node.js our Firebase functions run on is currently deprecated and will be decommissioned later this year (on October 30, 2025) - in order to preserve site functionality, we should upgrade the version of Node.js from the current 18 to 20.

Work Detail

• Upgrade the Node.js version for Firebase Functions from 18 to 20

Current State
Here is the PR for updating from Node 16 to 18 - the process should be identical: #1697

Additional Links

• Decommission dates for Node.js for Firebase Functions: https://cloud.google.com/functions/docs/runtime-support#node.js