tf/k8s-infra-prow-build-trusted: add ExternalSecrets

[spiffxp]

Related:

• Part of: Migrate all Opaque kubernetes Secrets on k8s-infra clusters to ExternalSecrets #2220
• Followup to: tf/k8s-infra-prow-build-trusted: add secrets #2859

The GSM secrets have been populated with values from the cluster, so these ExternalSecrets should be a no-op

[k8s-ci-robot]

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[spiffxp]

/cc @dims @BenTheElder

[dims]

/lgtm

[spiffxp]

Somehow this snuck by without a proper terraform apply. I picked up this change while deploying #3009

  # google_secret_manager_secret.build_cluster_secrets["k8s-infra-kops-e2e-tests-aws-ssh-key"] will be destroyed
  - resource "google_secret_manager_secret" "build_cluster_secrets" {
      - create_time = "2021-09-15T19:35:46.707338Z" -> null
      - id          = "projects/k8s-infra-prow-build-trusted/secrets/k8s-infra-kops-e2e-tests-aws-ssh-key" -> null
      - labels      = {
          - "group" = "sig-cluster-lifecycle"
        } -> null
      - name        = "projects/180382678033/secrets/k8s-infra-kops-e2e-tests-aws-ssh-key" -> null
      - project     = "k8s-infra-prow-build-trusted" -> null
      - secret_id   = "k8s-infra-kops-e2e-tests-aws-ssh-key" -> null

      - replication {
          - automatic = true -> null
        }

      - timeouts {}
    }

  # google_secret_manager_secret_iam_binding.build_cluster_secret_admins["k8s-infra-kops-e2e-tests-aws-ssh-key"] will be destroyed
  - resource "google_secret_manager_secret_iam_binding" "build_cluster_secret_admins" {
      - etag      = "BwXNGYe5/Yc=" -> null
      - id        = "projects/k8s-infra-prow-build-trusted/secrets/k8s-infra-kops-e2e-tests-aws-ssh-key/roles/secretmanager.admin" -> null
      - members   = [
          - "group:k8s-infra-kops-maintainers@kubernetes.io",
          - "group:k8s-infra-prow-oncall@kubernetes.io",
        ] -> null
      - project   = "k8s-infra-prow-build-trusted" -> null
      - role      = "roles/secretmanager.admin" -> null
      - secret_id = "projects/k8s-infra-prow-build-trusted/secrets/k8s-infra-kops-e2e-tests-aws-ssh-key" -> null
    }