Implemented plugin loading via di on the api server. Fixed plugin loading in the client

Moonlight.Client/Implementations/CoreStartup.cs

@@ -0,0 +1,17 @@
+using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
+using Moonlight.Client.Interfaces;
+
+namespace Moonlight.Client.Implementations;
+
+public class CoreStartup : IPluginStartup
+{
+    public Task BuildApplication(WebAssemblyHostBuilder builder)
+    {
+        builder.Services.AddSingleton<ISidebarItemProvider, DefaultSidebarItemProvider>();
+        
+        return Task.CompletedTask;
+    }
+
+    public Task ConfigureApplication(WebAssemblyHost app)
+        => Task.CompletedTask;
+}