Create CI/CD Pipeline for GCP Deployment

[lb4368]

Problem description
Per issues #564 and #575 a common site type and phase plan will be created for use by all provider types. We need a CI/CD pipeline which validates end-to-end phase plan deployment of target cluster using CAPG provider using this common site type.

Proposed change
Build a CI/CD pipeline which demonstrates successful end-to-end deployment of gcp-test-site leveraging the common gating type created via #575 and configured with phase/plan overrides specific for the CAPG provider.