feat(networkservices): add DNS peering config to AgentGateway:

mmv1/products/networkservices/AgentGateway.yaml

@@ -175,6 +175,35 @@ properties:
             diff_suppress_func: 'tpgresource.ProjectNumberDiffSuppress'
             description: |
               The URI of the Network Attachment resource.
+      - name: 'dnsPeeringConfig'
+        type: NestedObject
+        description: |
+          DNS peering configuration for the AgentGateway. When set, the
+          AgentGateway will resolve queries for the configured `domains` via
+          Cloud DNS in the specified `targetNetwork`.
+        properties:
+          - name: 'domains'
+            type: Array
+            required: true
+            description: |
+              The list of domain names to peer for DNS resolution. Each entry
+              must be a fully qualified domain name ending with a dot
+              (for example, `example.com.`).
+            item_type:
+              type: String
+          - name: 'targetProject'
+            type: String
+            required: true
+            description: |
+              The ID of the project that hosts the target VPC network for DNS
+              peering.
+          - name: 'targetNetwork'
+            type: String
+            required: true
+            diff_suppress_func: 'tpgresource.CompareSelfLinkOrResourceName'
+            description: |
+              The URI of the target VPC network for DNS peering. Must be of the
+              form `projects/{project}/global/networks/{network}`.
   - name: 'agentGatewayCard'
     type: NestedObject
     description: |

mmv1/templates/terraform/examples/network_services_agent_gateway_full.tf.tmpl

@@ -20,5 +20,10 @@ resource "google_network_services_agent_gateway" "{{$.PrimaryResourceId}}" {
     egress {
       network_attachment = "projects/{{index $.TestEnvVars "project"}}/regions/us-central1/networkAttachments/my-network-attachment"
     }
+    dns_peering_config {
+      domains        = ["example.com."]
+      target_project = "{{index $.TestEnvVars "project"}}"
+      target_network = "projects/{{index $.TestEnvVars "project"}}/global/networks/my-network"
+    }
   }
 }

mmv1/third_party/terraform/services/networkservices/resource_network_services_agent_gateway_test.go.tmpl

@@ -100,6 +100,11 @@ resource "google_network_services_agent_gateway" "default" {
     egress {
       network_attachment = "projects/%{project}/regions/us-central1/networkAttachments/oh-my-network-attachment"
     }
+    dns_peering_config {
+      domains        = ["update.example.com."]
+      target_project = "%{project}"
+      target_network = "projects/%{project}/global/networks/oh-my-network"
+    }
   }
 }
 `, context)