initial GCP support

I include very initial support for Google Cloud Platform. I've been able to do the 'terraform apply', 'make tools' and 'make testnet-validator' successfully, with the following caveats:

(1) The testnet isn't running right now so I didn't really do much testing. I verified that binance-daemon was syncing and that I could launch various dashboards, e.g., "make grafana". I didn't actually check the data behind the dashboards.

(2) I had to edit the Makefile in node-launcher and comment out where helm starts the metrics-server. The terraform step launches a metrics-server in GCP so the helm step gets confused. I'm not sure what this breaks.

(3) I didn't do anything with security at all. I'm pretty sure the nodes have externally reachable IPs by default.

I don't recommend adding this to the cluster-launcher/Makefile at this stage. I think it's a good enough start so that people can play with it if they know what they are doing or, even better, someone who actually knows what they are doing will look at it in disgust and just fix it. But for now, I don't think it is a good idea to make it easy for someone to use.