Implement GCP Batch Support

[jmchilton]

Reviewing the docs @ https://cloud.google.com/batch/docs/reference/rest/v1alpha/projects.locations.jobs/create - it looks much closer to K8S & TES than AWS Batch (e.g. single document describing multiple containers) - so it should be easier to implement support for it here.

[domgz]

I think the ARC integration I am developing has at least some loose similarities. It would be nice if you ask me for a review when you open the PR (just to feel pressured to have a look and see how you did it, ofc you may ask more people to review). I'll do the same.