Automate the creation of the Marauder group + Adding service accounts to it

I had [a lot of trouble](https://serverfault.com/questions/1016100/programatically-managing-groups-users-in-gsuite-via-the-api) getting the GSuite API to work, so, unfortunately users currently need to manually create a group and add the service accounts to it.

I've tried to make it as painless as possible, but I'd really like to automate the gcloud_init script to do all that.