add(IFriendService)：完善好友关系接口

backend/IM_API/Dtos/HandleFriendRequestDto.cs

@@ -0,0 +1,25 @@
+namespace IM_API.Dtos
+{
+    public class HandleFriendRequestDto
+    {
+        /// <summary>
+        /// 好友请求Id
+        /// </summary>
+        public int RequestId { get; set; }
+        /// <summary>
+        /// 处理操作
+        /// </summary>
+        public HandleFriendRequestAction Action { get; set; }
+    }
+    public enum HandleFriendRequestAction
+    {
+        /// <summary>
+        /// 同意
+        /// </summary>
+        Accept = 0,
+        /// <summary>
+        /// 拒绝
+        /// </summary>
+        Reject = 1
+    }
+}