feat(work): 新增同步客服消息相关接口

src/SKIT.FlurlHttpClient.Wechat.Work/Events/KfMessage/KfMessageEvent.cs

@@ -0,0 +1,16 @@
+namespace SKIT.FlurlHttpClient.Wechat.Work.Events
+{
+    /// <summary>
+    /// <para>表示 kf_msg_or_event 事件的数据。</para>
+    /// <para>REF: https://open.work.weixin.qq.com/api/doc/90000/90135/94670 </para>
+    /// <para>REF: https://open.work.weixin.qq.com/api/doc/90001/90143/94699 </para>
+    /// </summary>
+    public class KfMessageEvent : WechatWorkEvent, WechatWorkEvent.Types.IXmlSerializable
+    {
+        /// <summary>
+        /// 获取或设置调用拉取消息的 Token。
+        /// </summary>
+        [System.Xml.Serialization.XmlElement("Content")]
+        public string Token { get; set; } = default!;
+    }
+}