Create common interface for SyncPlay requests

MediaBrowser.Controller/SyncPlay/Requests/JoinGroupRequest.cs

@@ -0,0 +1,29 @@
+using System;
+using MediaBrowser.Model.SyncPlay;
+
+namespace MediaBrowser.Controller.SyncPlay.Requests
+{
+    /// <summary>
+    /// Class JoinGroupRequest.
+    /// </summary>
+    public class JoinGroupRequest : ISyncPlayRequest
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="JoinGroupRequest"/> class.
+        /// </summary>
+        /// <param name="groupId">The identifier of the group to join.</param>
+        public JoinGroupRequest(Guid groupId)
+        {
+            GroupId = groupId;
+        }
+
+        /// <summary>
+        /// Gets the group identifier.
+        /// </summary>
+        /// <value>The identifier of the group to join.</value>
+        public Guid GroupId { get; }
+
+        /// <inheritdoc />
+        public RequestType Type { get; } = RequestType.JoinGroup;
+    }
+}