[FEATURE] GDrive auth workflow improvements

[chrismclarke]

What?
Following discussions in #2544, it would be good to reconsider how best to manage authenticating developers to sync content from gdrive

Why?
The current workflow relies on using application credentials stored locally in the repo (encrypted, so require all developers to be provided a private key to decrypt, independent of additional private keys need for deployments)

How?
It might be possible to deploy our auth scripts as a lightweight cloud function where the application credentials can be stored securely as part of the build. We also need to consider whether we want all developers using these credentials/endpoints, or using their own (there are some limits to how many requests can be made from a set of credentials).

Other details
Google auth docs
NodeJS auth client docs