Added diagnose frontend and backend implementation

Moonlight.Api/Implementations/UpdateDiagnoseProvider.cs

@@ -0,0 +1,33 @@
+using Moonlight.Api.Interfaces;
+using Moonlight.Api.Models;
+using Moonlight.Api.Services;
+
+namespace Moonlight.Api.Implementations;
+
+public sealed class UpdateDiagnoseProvider : IDiagnoseProvider
+{
+    private readonly ApplicationService ApplicationService;
+
+    public UpdateDiagnoseProvider(ApplicationService applicationService)
+    {
+        ApplicationService = applicationService;
+    }
+
+    public Task<DiagnoseResult[]> DiagnoseAsync()
+    {
+        if (ApplicationService.IsUpToDate)
+            return Task.FromResult<DiagnoseResult[]>([]);
+
+        return Task.FromResult<DiagnoseResult[]>([
+            new DiagnoseResult(
+                DiagnoseLevel.Warning,
+                "Instance is not up-to-date",
+                ["Moonlight", "Update Check"],
+                "Update your moonlight instance to receive bug fixes, new features and security patches. Update button can be found in the overview",
+                null,
+                "/admin",
+                null
+            )
+        ]);
+    }
+}