[FIX] pos_self_order: kiosk print receipt when nothing to pay

Before this commit:
===================
If there is an order with a total amount of 0 in kiosk mode, then after the cart
page it is redirected to the home page without printing a receipt.

After this commit:
==================
with this commit, if an order amount is 0 then it will redirect to the
confirmation/receipt page like a normal order with the amount without
redirecting to the payment page.

task - 3773450

closes odoo/odoo#155826

Signed-off-by: Quentin Lejeune (qle) <qle@odoo.com>

addons/pos_self_order/static/src/app/components/order_widget/order_widget.js

@@ -58,10 +58,6 @@ export class OrderWidget extends Component {
             disabled = !kioskPayment && !isMobilePayment;
         }
 
-        if (this.selfOrder.currentOrder.amount_total === 0) {
-            label = _t("Order");
-        }
-
         return { label, disabled };
     }
 

addons/pos_self_order/static/src/app/self_order_service.js

@@ -195,11 +195,22 @@ export class SelfOrder extends Reactive {
     }
 
     get currentOrder() {
-        if (this.editedOrder && this.editedOrder.state === "draft") {
+        if (
+            this.editedOrder &&
+            (this.editedOrder.state === "draft" ||
+                (this.editedOrder.state === "paid" &&
+                    this.editedOrder.amount_total === 0 &&
+                    this.config.self_ordering_mode === "kiosk"))
+        ) {
             return this.editedOrder;
         }
-
-        const existingOrder = this.orders.find((o) => o.state === "draft");
+        const existingOrder = this.orders.find(
+            (o) =>
+                o.state === "draft" ||
+                (o.state === "paid" &&
+                    o.amount_total === 0 &&
+                    this.config.self_ordering_mode === "kiosk")
+        );
         if (!existingOrder) {
             const newOrder = new Order({
                 pos_config_id: this.pos_config_id,