POS: Add item list to keypad (#5814)

* Add admin option to show item list for keypad view

* Refactor common POS Vue mixin

* Add item list to POS keypad

* Add recent transactions to cart

* Keypad: Pass tip and discount as cart does

* Keypad and cart tests

* Improve offcanvas button

---------

Co-authored-by: Andrew Camilleri <evilkukka@gmail.com>

BTCPayServer/Controllers/GreenField/GreenfieldAppsController.cs

@@ -274,6 +274,7 @@ namespace BTCPayServer.Controllers.Greenfield
             {
                 Title = request.Title ?? request.AppName,
                 DefaultView = (PosViewType)request.DefaultView,
+                ShowItems = request.ShowItems,
                 ShowCustomAmount = request.ShowCustomAmount,
                 ShowDiscount = request.ShowDiscount,
                 ShowSearch = request.ShowSearch,
@@ -335,6 +336,7 @@ namespace BTCPayServer.Controllers.Greenfield
                 Created = appData.Created,
                 Title = settings.Title,
                 DefaultView = settings.DefaultView.ToString(),
+                ShowItems = settings.ShowItems,
                 ShowCustomAmount = settings.ShowCustomAmount,
                 ShowDiscount = settings.ShowDiscount,
                 ShowSearch = settings.ShowSearch,