fix: Update expressmode api call to include default api key param

Express mode API was updated to require "get_default_api_key: True" for returning api key

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 912153767

Author: wukath

src/google/adk/cli/utils/gcp_utils.py

@@ -139,7 +139,11 @@ def sign_up_express(
       "POST",
       ":signUp",
       location=location,
-      data={"region": location, "tos_accepted": True},
+      data={
+          "region": location,
+          "tos_accepted": True,
+          "get_default_api_key": True,
+      },
   )
   return {
       "project_id": project.get("projectId"),

tests/unittests/cli/utils/test_gcp_utils.py

@@ -126,11 +126,19 @@ def test_sign_up_express(self, mock_auth_default, mock_session_cls):
     result = gcp_utils.sign_up_express()
     self.assertEqual(result["project_id"], "new-project")
     self.assertEqual(result["api_key"], "new-api-key")
-    args, _ = mock_session.post.call_args
+    args, kwargs = mock_session.post.call_args
     self.assertEqual(
         args[0],
         "https://us-central1-aiplatform.googleapis.com/v1beta1/vertexExpress:signUp",
     )
+    self.assertEqual(
+        kwargs["json"],
+        {
+            "region": "us-central1",
+            "tos_accepted": True,
+            "get_default_api_key": True,
+        },
+    )
 
   @mock.patch(
       "google.adk.cli.utils.gcp_utils.resourcemanager_v3.ProjectsClient"