Create GHA CI workflow to test k8ssandra-terraform GCP module

[sync-by-unito]

A CI workflow should be created in GHA to test the GCP Terraform module for K8ssandra.
The workflow should be scheduled every week and would provision a GKE cluster on which the latest stable version of K8ssandra would be deployed.
Smoke tests should be implemented to verify that all the components have started successfully:

• Check that the cassdc object reaches "Ready" state
• Check that Cassandra is accessible by running cqlsh
• Check that Stargate is accessible through its REST api
• Check that Reaper is accessible through its REST api
• Check that Grafana is accessible through its Web UI
  Medusa is assumed to be in a working state if Cassandra is accessible.

┆Issue is synchronized with this Jiraserver Task by Unito
┆Epic: k8ssandra-terraform integration tests
┆Issue Number: K8SSAND-575
┆Priority: Medium

[chaitu6022]

We need to create a service account save the service account credentials in the GitHub secrets.