add advanced_datapath_observability_config support (#3945)

Adds support for `advanced_datapath_observability_config` to the `gke-cluster-autopilot` module, matching the standard cluster module implementation.

Closes #3936

TAG=agy
CONV=9d4485ab-0fae-4f3d-a6e1-bbb6320d7c46

tests/modules/gke_cluster_autopilot/monitoring.tfvars

@@ -0,0 +1,13 @@
+project_id = "my-project"
+location   = "europe-west1"
+name       = "cluster-1"
+vpc_config = {
+  network    = "default"
+  subnetwork = "default"
+}
+monitoring_config = {
+  advanced_datapath_observability = {
+    enable_metrics = true
+    enable_relay   = true
+  }
+}

tests/modules/gke_cluster_autopilot/monitoring.yaml

@@ -0,0 +1,23 @@
+# Copyright 2025 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:
+  google_container_cluster.cluster:
+    monitoring_config:
+    - advanced_datapath_observability_config:
+      - enable_metrics: true
+        enable_relay: true
+
+counts:
+  google_container_cluster: 1

tests/modules/gke_cluster_autopilot/tftest.yaml

@@ -16,3 +16,4 @@ module: modules/gke-cluster-autopilot
 
 tests:
   network_tags:
+  monitoring: