Implemented basic ui for server sharing. Extracted server authorization. Refactoring and small improvements

MoonlightServers.ApiServer/Interfaces/IServerAuthorizationFilter.cs

@@ -0,0 +1,17 @@
+using System.Security.Claims;
+using MoonlightServers.ApiServer.Database.Entities;
+using MoonlightServers.ApiServer.Models;
+using MoonlightServers.Shared.Models;
+
+namespace MoonlightServers.ApiServer.Interfaces;
+
+public interface IServerAuthorizationFilter
+{
+    // Return null => skip to next filter / handler
+    // Return any value, instant return
+    public Task<ServerAuthorizationResult?> Process(
+        ClaimsPrincipal user,
+        Server server,
+        Func<ServerSharePermission, bool>? filter = null
+    );
+}