feat: add PluginLoadReason to plugin interface

Dalamud/Plugin/PluginLoadReason.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Dalamud.Plugin
+{
+    /// <summary>
+    /// This enum reflects reasons for loading a plugin.
+    /// </summary>
+    public enum PluginLoadReason
+    {
+        /// <summary>
+        /// We don't know why this plugin was loaded.
+        /// </summary>
+        Unknown,
+
+        /// <summary>
+        /// This plugin was loaded because it was installed with the plugin installer.
+        /// </summary>
+        Installer,
+
+        /// <summary>
+        /// This plugin was loaded because the game was started or Dalamud was reinjected.
+        /// </summary>
+        Boot
+    }
+}