google access token to be stored in-memory

[tomholub]

In another issue: switch access token to be also stored in-memory instead of storage.

Originally posted by @tomholub in #4194 (comment)

similar/same as how id token is stored in memory

[tomholub]

will need to also update additional settings -> experimental -> wipe access token

google_access_token should be removed from local storage model

I don't think we need to actually wipe it from local storage (no need to do migration) since these access tokens are short lived. It will just expire.

[tomholub]

This is for after #4194 / #4195 lands.