Set Artifact Registry visibility as public in Terraform

[bourgeoisor]

Currently, the IaC Terraform script for the CI/CD pipeline creates a private Artifact Registry repository.

https://github.com/GoogleCloudPlatform/bank-of-anthos/blob/main/iac/tf-multienv-cicd-anthos-autopilot/artifact-registry.tf

The above need to be augmented such that the member allUsers has role roles/artifactregistry.reader.

[bourgeoisor]

This is still important to do.