feat(wxapi): 新增微信长辈就医相关接口

src/SKIT.FlurlHttpClient.Wechat.Api/Models/CityService/CityServiceGetMessageRelationResponse.cs

@@ -0,0 +1,17 @@
+namespace SKIT.FlurlHttpClient.Wechat.Api.Models
+{
+    /// <summary>
+    /// <para>表示 [POST] /cityservice/getmsgrelation 接口的响应。</para>
+    /// </summary>
+    public class CityServiceGetMessageRelationResponse : WechatApiResponse
+    {
+        /// <summary>
+        /// 获取或设置是否已订阅。
+        /// </summary>
+        [Newtonsoft.Json.JsonProperty("is_subscribed")]
+        [Newtonsoft.Json.JsonConverter(typeof(Newtonsoft.Json.Converters.Common.NumericalBooleanReadOnlyConverter))]
+        [System.Text.Json.Serialization.JsonPropertyName("is_subscribed")]
+        [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Serialization.Common.NumericalBooleanReadOnlyConverter))]
+        public bool IsSubscribed { get; set; }
+    }
+}