docs: added customer storefront guides (#7685)

* added customer guides

* fixes to sidebar

* remove old customer registration guide

* fix build error

* generate files

* run linter

www/apps/resources/app/commerce-modules/promotion/page.mdx

@@ -24,7 +24,7 @@ const promotion = await promotionModuleService.create({
     type: "percentage",
     target_type: "order",
     value: "10",
-    currency_code: "usd"
+    currency_code: "usd",
   },
 })
 ```
@@ -41,7 +41,7 @@ const promotion = await promotionModuleService.create({
     type: "percentage",
     target_type: "order",
     value: "10",
-    currency_code: "usd"
+    currency_code: "usd",
   },
   rules: [
     {