Add default value to env.value to fix the plan diffs in cloud run services (GoogleCloudPlatform#13363)

Author: zli82016

mmv1/products/cloudrun/Service.yaml

@@ -451,6 +451,10 @@ properties:
                             description: Name of the environment variable.
                           - name: 'value'
                             type: String
+                            # env is a set.
+                            # The env.value has value "" in Terraform state, but it has value nil in Terraform plan,
+                            # which causes the diffs for unchanged env. default_value: "" is to suppress the diffs.
+                            default_value: ""
                             description: |-
                               Defaults to "".
                           - name: 'valueFrom'

mmv1/products/cloudrunv2/Service.yaml

@@ -481,6 +481,10 @@ properties:
                     required: true
                   - name: 'value'
                     type: String
+                    # env is a set.
+                    # The env.value has value "" in Terraform state, but it has value nil in Terraform plan,
+                    # which causes the diffs for unchanged env. default_value: "" is to suppress the diffs.
+                    default_value: ""
                     description: |-
                       Literal value of the environment variable. Defaults to "" and the maximum allowed length is 32768 characters. Variable references are not supported in Cloud Run.
                     # exactly_one_of: