Modify Terraform Job to Allow Single and Multi Node Geo Configurations

Summary

The GitLab Orchestrator tool currently performs the following using Terraform:

• Creates 7 VM instances in GCP for a Geo primary cluster: 3 x Consul nodes, 3 x Postgres nodes and 1 x application node
• Creates 7 VM instances in GCP for a Geo secondary cluster: 3 x Consul nodes, 3 x Postgres nodes and 1 x application node
• Installs GitLab on each of the nodes

This issue addresses the next step, which is to tag each node as being either part of the primary cluster or part of the secondary cluster so that the nodes are separated into two distinct clusters for Geo.

The tags should translate into something parseable by Ansible's inventory.