feat: Chat webhook (#605)

* feat: add chat webhook app

* improve indentation

---------

Co-authored-by: pierrick <pierrick@google.com>

Author: PierrickVoulet

solutions/webhook-chat-app/README.md

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+# Google Chat App Webhook
+
+Please see related guide on how to
+[send messages to Google Chat with incoming webhooks](https://developers.google.com/workspace/chat/quickstart/webhooks).

solutions/webhook-chat-app/thread-reply.gs

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+/**
+ * Copyright 2023 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.
+ */
+
+
+// [START chat_webhook_thread]
+function webhook() {
+  const url = "https://chat.googleapis.com/v1/spaces/SPACE_ID/messages?key=KEY&token=TOKEN&messageReplyOption=REPLY_MESSAGE_FALLBACK_TO_NEW_THREAD"
+  const options = {
+    "method": "post",
+    "headers": {"Content-Type": "application/json; charset=UTF-8"},
+    "payload": JSON.stringify({
+      "text": "Hello from Apps Script!",
+      "thread": {
+        "threadKey": "THREAD_KEY_VALUE"
+      }
+    })
+  };
+  const response = UrlFetchApp.fetch(url, options);
+  console.log(response);
+}
+// [END chat_webhook_thread]

solutions/webhook-chat-app/webhook.gs

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+/**
+ * Copyright 2022 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.
+ */
+
+
+// [START chat_webhook]
+function webhook() {
+  const url = "https://chat.googleapis.com/v1/spaces/SPACE_ID/messages?key=KEY&token=TOKEN"
+  const options = {
+    "method": "post",
+    "headers": {"Content-Type": "application/json; charset=UTF-8"},
+    "payload": JSON.stringify({
+      "text": "Hello from Apps Script!"
+    })
+  };
+  const response = UrlFetchApp.fetch(url, options);
+  console.log(response);
+}
+// [END chat_webhook]