Migrate ServerEventNotifier.OnPackageInstalling to IEventConsumer

MediaBrowser.Controller/Events/Updates/PluginInstallingEventArgs.cs

@@ -0,0 +1,19 @@
+using Jellyfin.Data.Events;
+using MediaBrowser.Model.Updates;
+
+namespace MediaBrowser.Controller.Events.Updates
+{
+    /// <summary>
+    /// An event that occurs when a plugin is installing.
+    /// </summary>
+    public class PluginInstallingEventArgs : GenericEventArgs<InstallationInfo>
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PluginInstallingEventArgs"/> class.
+        /// </summary>
+        /// <param name="arg">The installation info.</param>
+        public PluginInstallingEventArgs(InstallationInfo arg) : base(arg)
+        {
+        }
+    }
+}