Reworked encryption to use less heap allocated buffers for secrets.

Also some work on plugin system.

IdentityShroud.Core/Plugins/PluginRegistry.cs

@@ -0,0 +1,18 @@
+using System.Collections.ObjectModel;
+using IdentityShroud.PluginSupport;
+
+namespace IdentityShroud.Core.Plugins;
+
+/// <summary>
+/// Note 
+/// </summary>
+/// <typeparam name="TPlugin"></typeparam>
+public class PluginRegistry<TPlugin> where TPlugin : IPlugin
+{
+    private ReadOnlyDictionary<string, TPlugin> _plugins;
+
+    public PluginRegistry(ReadOnlyDictionary<string, TPlugin> plugins)
+    {
+        _plugins = plugins;
+    }
+}