Resolve "Adding LB config for load-balanced Cloud Run services"
The MR has breaking changes so I've set the target branch to https://gitlab.developers.cam.ac.uk/uis/devops/infra/terraform/gcp-cloud-run-app/-/tree/v4.
Basically, the MR sets up a Load Balancer for the Cloud Run service when the variable use_cloud_load_balancer is set to true.
Closes #24 (closed)