Checkout: Display description if present (#6082)

This is mostly for the POS, where either an individual item title might be the description, or in case of the cart and keypad, the name of the app will be displayed. The description is omitted if it matches the store name, to avoid duplicate titles.

Closes #5023.

BTCPayServer/Views/UIInvoice/Checkout.cshtml

@@ -52,6 +52,7 @@
                 </button>
             </nav>
             <section id="payment" v-if="isActive">
+                <div v-if="srvModel.itemDesc && srvModel.itemDesc !== srvModel.storeName" v-text="srvModel.itemDesc" class="fw-semibold text-center text-muted mb-3"></div>
                 <div class="d-flex justify-content-center mt-1 text-center">
                     @if (Model.IsUnsetTopUp)
                     {