Upgrade to Cloud Functions v2 - when available

[akauppi]

Currently in public preview, there are still some omissions:

• [ ] Cloud Firestore triggers

When those are available, move to v2.

[akauppi]

Note: CPU consumption in v2 seems highly different.

• make a note in the code
• https://firebase.google.com/docs/functions/beta/manage-functions#override-CPU
• setGlobalOptions({ cpu: 'gcfv1' });