Started implementing metrics system

Moonlight.ApiServer/Implementations/Metrics/UsersMetric.cs

@@ -0,0 +1,27 @@
+using System.Diagnostics.Metrics;
+using Microsoft.EntityFrameworkCore;
+using MoonCore.Extended.Abstractions;
+using Moonlight.ApiServer.Database.Entities;
+using Moonlight.ApiServer.Interfaces;
+
+namespace Moonlight.ApiServer.Implementations.Metrics;
+
+public class UsersMetric : IMetric
+{
+    private Gauge<int> Users;
+    
+    public Task Initialize(Meter meter)
+    {
+        Users = meter.CreateGauge<int>("moonlight_users");
+        
+        return Task.CompletedTask;
+    }
+
+    public async Task Run(IServiceProvider provider, CancellationToken cancellationToken)
+    {
+        var usersRepo = provider.GetRequiredService<DatabaseRepository<User>>();
+        var count = await usersRepo.Get().CountAsync(cancellationToken: cancellationToken);
+        
+        Users.Record(count);
+    }
+}