docs: improve payment related guides (#12502)

* improve guide

* update guides

* small change

www/apps/resources/generated/generated-commerce-modules-sidebar.mjs

@@ -9081,6 +9081,14 @@ const generatedgeneratedCommerceModulesSidebarSidebar = {
               "title": "Payment Module Provider",
               "children": []
             },
+            {
+              "loaded": true,
+              "isPathHref": true,
+              "type": "link",
+              "path": "/commerce-modules/payment/payment-checkout-flow",
+              "title": "Payment in Checkout",
+              "children": []
+            },
             {
               "loaded": true,
               "isPathHref": true,