Implement side story + move jsondb class

nksrv/LobbyServer/Msgs/Sidestory/EnterBattle.cs

@@ -0,0 +1,19 @@
+using nksrv.Net;
+using nksrv.Utils;
+
+namespace nksrv.LobbyServer.Msgs.Sidestory
+{
+    [PacketPath("/sidestory/cut/enterbattle")]
+    public class EnterBattle : LobbyMsgHandler
+    {
+        protected override async Task HandleAsync()
+        {
+            var req = await ReadData<ReqEnterSideStoryCutForBattle>();
+            var user = GetUser();
+
+            var response = new ResEnterSideStoryCutForBattle();
+
+            await WriteDataAsync(response);
+        }
+    }
+}