POS: Option for user sign in via the QR code (#6231)

* Login Code: Turn into Blazor component and extend with data for the app

* POS: Add login code for POS frontend

* Improve components, fix test

BTCPayServer/Plugins/PointOfSale/Models/UpdatePointOfSaleViewModel.cs

@@ -68,6 +68,7 @@ namespace BTCPayServer.Plugins.PointOfSale.Models
         public string CustomTipPercentages { get; set; }
 
         public string Id { get; set; }
+        public Dictionary<string, string> StoreUsers { get; set; }
 
         [Display(Name = "Redirect invoice to redirect url automatically after paid")]
         public string RedirectAutomatically { get; set; } = string.Empty;