feat: 飞书适配器加入“机器人进群欢迎语”配置 (#1852)

* feat(lark): 支持机器人进群发送欢迎消息

* perf: existence check and indent

---------

Co-authored-by: donghao <donghao@patsnap.com>
Co-authored-by: Junyan Qin <rockchinq@gmail.com>

src/langbot/pkg/platform/sources/lark.yaml

@@ -65,6 +65,16 @@ spec:
       type: boolean
       required: true
       default: false
+    - name: bot_added_welcome
+      label:
+        en_US: Bot Welcome Message
+        zh_Hans: 机器人进群欢迎语
+      description:
+        en_US: Welcome message when the bot is added to a group, supports Markdown format
+        zh_Hans: 机器人进群欢迎语，支持 Markdown 格式
+      type: text
+      required: false
+      default: ""
 execution:
   python:
     path: ./lark.py