Upgrade Cloud Functions from gen1 to gen2

[spbnick]

Google has implemented a new interface for Cloud Functions called "gen2", and is calling the previous interface "gen1". It's likely that the support for the latter is going to peter out after a while, so we need to migrate. The "gen2" functions have more features and better performance for some cases too.

Here's the official comparison: https://cloud.google.com/functions/docs/concepts/version-comparison