fix: Add missing config ID to RestTransportTest push notification test

The testSetTaskPushNotificationConfiguration was failing because the
PushNotificationConfig was created without an ID. This caused the
request to not match the expected protobuf format which requires both
a configId field and the ID in the resource name path.

Changes:
- Added .id("default-config-id") to PushNotificationConfig.Builder in RestTransportTest.java
- Updated SET_TASK_PUSH_NOTIFICATION_CONFIG_TEST_REQUEST in JsonRestMessages.java to include:
  - configId field at top level
  - Full resource name with config ID in path: tasks/{taskId}/pushNotificationConfigs/{configId}

This matches the pattern used in the working JSONRPCTransportTest.

Test now passes: ✅ RestTransportTest.testSetTaskPushNotificationConfiguration

Author: ehsavoie

client/transport/rest/src/test/java/io/a2a/client/transport/rest/JsonRestMessages.java

@@ -347,8 +347,9 @@ public class JsonRestMessages {
     static final String SET_TASK_PUSH_NOTIFICATION_CONFIG_TEST_REQUEST = """
             {
               "parent": "tasks/de38c76d-d54c-436c-8b9f-4c2703648d64",
+              "configId": "default-config-id",
               "config": {
-                "name": "tasks/de38c76d-d54c-436c-8b9f-4c2703648d64/pushNotificationConfigs",
+                "name": "tasks/de38c76d-d54c-436c-8b9f-4c2703648d64/pushNotificationConfigs/default-config-id",
                 "pushNotificationConfig": {
                   "url": "https://example.com/callback",
                   "authentication": {

client/transport/rest/src/test/java/io/a2a/client/transport/rest/RestTransportTest.java

@@ -304,6 +304,7 @@ public void testSetTaskPushNotificationConfiguration() throws Exception {
         TaskPushNotificationConfig pushedConfig = new TaskPushNotificationConfig(
                 "de38c76d-d54c-436c-8b9f-4c2703648d64",
                 new PushNotificationConfig.Builder()
+                        .id("default-config-id")
                         .url("https://example.com/callback")
                         .authenticationInfo(
                                 new AuthenticationInfo(Collections.singletonList("jwt"), null))