feat(feishu): add configurable domain for Lark international support (#1535)

The lark-oapi SDK defaults to open.feishu.cn (China), but apps on the
international Lark platform (open.larksuite.com) fail to connect with
error 1000040351 'Incorrect domain name'.

Changes:
- Add 'domain' config option to feishu channel (default: open.feishu.cn)
- Pass domain to both API client and WebSocket client
- Update config.example.yaml and all README files

README_zh.md

@@ -255,6 +255,8 @@ channels:
     enabled: true
     app_id: $FEISHU_APP_ID
     app_secret: $FEISHU_APP_SECRET
+    # domain: https://open.feishu.cn       # 国内版（默认）
+    # domain: https://open.larksuite.com   # 国际版
 
   slack:
     enabled: true