Replace `google_project_iam_binding` with `google_project_iam_member`

[NimJay]

• google_project_iam_binding is "authoritative for a given role". This means that pre-existing bindings (to the role being modified by google_project_iam_binding) will be removed.
  • See related Terraform documentation here.
  • See related GitHub Issue.
• We would have to replace the use of google_project_iam_binding (e.g., inside infra/iam.tf) with google_project_iam_member.
• This migration is also recommended by the cloud.google.com Terraform Best Practices — followed by Blueprints.