Allow using no service account in compute-vm (#1692)

* module and tests

* align blueprints

* tfdoc

* remove stale variables

* fix blueprint

* variable description

tests/modules/compute_vm/examples/sa-default.yaml

@@ -0,0 +1,79 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+values:
+  module.vm-managed-sa-example.google_compute_instance.default[0]:
+    advanced_machine_features: []
+    allow_stopping_for_update: true
+    attached_disk: []
+    boot_disk:
+    - auto_delete: true
+      disk_encryption_key_raw: null
+      initialize_params:
+      - image: projects/debian-cloud/global/images/family/debian-11
+        resource_manager_tags: null
+        size: 10
+        type: pd-balanced
+      mode: READ_WRITE
+    can_ip_forward: false
+    deletion_protection: false
+    description: Managed by the compute-vm Terraform module.
+    desired_status: null
+    enable_display: false
+    hostname: null
+    labels: null
+    machine_type: f1-micro
+    metadata: null
+    metadata_startup_script: null
+    name: test1
+    network_interface:
+    - access_config: []
+      alias_ip_range: []
+      ipv6_access_config: []
+      network: projects/xxx/global/networks/aaa
+      nic_type: null
+      queue_count: null
+      subnetwork: subnet_self_link
+    network_performance_config: []
+    params: []
+    project: project-id
+    resource_policies: null
+    scheduling:
+    - automatic_restart: true
+      instance_termination_action: null
+      local_ssd_recovery_timeout: []
+      maintenance_interval: null
+      max_run_duration: []
+      min_node_cpus: null
+      node_affinities: []
+      on_host_maintenance: MIGRATE
+      preemptible: false
+      provisioning_model: STANDARD
+    scratch_disk: []
+    service_account:
+    - scopes:
+      - https://www.googleapis.com/auth/devstorage.read_only
+      - https://www.googleapis.com/auth/logging.write
+      - https://www.googleapis.com/auth/monitoring.write
+    shielded_instance_config: []
+    tags: null
+    timeouts: null
+    zone: europe-west1-b
+
+counts:
+  google_compute_instance: 1
+  modules: 1
+  resources: 1
+
+outputs: {}