feat: add create membership for group code sample

chat/client-libraries/cloud/src/main/java/com/google/workspace/api/chat/samples/CreateMembershipUserCredForGroup.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2024 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
+ *
+ *      https://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.
+ */
+
+package com.google.workspace.api.chat.samples;
+
+import com.google.common.collect.ImmutableList;
+import com.google.protobuf.util.JsonFormat;
+// [START chat_create_membership_user_cred_for_group]
+import com.google.chat.v1.ChatServiceClient;
+import com.google.chat.v1.CreateMembershipRequest;
+import com.google.chat.v1.Membership;
+import com.google.chat.v1.SpaceName;
+import com.google.chat.v1.Group;
+
+// This sample shows how to create membership with user credential for a group.
+public class CreateMembershipUserCredForGroup {
+
+  private static final String SCOPE =
+    "https://www.googleapis.com/auth/chat.memberships";
+
+  public static void main(String[] args) throws Exception {
+    try (ChatServiceClient chatServiceClient =
+        AuthenticationUtils.createClientWithUserCredentials(
+          ImmutableList.of(SCOPE))) {
+      CreateMembershipRequest.Builder request = CreateMembershipRequest.newBuilder()
+        // replace SPACE_NAME here
+        .setParent("spaces/SPACE_NAME")
+        .setMembership(Membership.newBuilder()
+          .setGroupMember(Group.newBuilder()
+            // replace GROUP_NAME here
+            .setName("groups/GROUP_NAME")));
+      Membership response = chatServiceClient.createMembership(request.build());
+
+      System.out.println(JsonFormat.printer().print(response));
+    }
+  }
+}
+// [END chat_create_membership_user_cred_for_group]