docs: added how-to guides for architectural modules (#11883)

* added initial how-tos

* finished changes

* generated sidebars

www/apps/resources/references/_index.mdx

@@ -9,6 +9,7 @@ import { TypeList } from "docs-ui"
 - [auth](modules/auth/page.mdx)
 - [auth-models](modules/auth_models/page.mdx)
 - [auth-provider](modules/auth_provider/page.mdx)
+- [cache](modules/cache/page.mdx)
 - [cart](modules/cart/page.mdx)
 - [cart-models](modules/cart_models/page.mdx)
 - [core-flows](modules/core_flows/page.mdx)
@@ -17,7 +18,9 @@ import { TypeList } from "docs-ui"
 - [customer](modules/customer/page.mdx)
 - [customer-models](modules/customer_models/page.mdx)
 - [dml](modules/dml/page.mdx)
+- [event](modules/event/page.mdx)
 - [file](modules/file/page.mdx)
+- [file-service](modules/file_service/page.mdx)
 - [fulfillment](modules/fulfillment/page.mdx)
 - [fulfillment-models](modules/fulfillment_models/page.mdx)
 - [fulfillment-provider](modules/fulfillment_provider/page.mdx)
@@ -30,6 +33,7 @@ import { TypeList } from "docs-ui"
 - [medusa-config](modules/medusa_config/page.mdx)
 - [modules-sdk](modules/modules_sdk/page.mdx)
 - [notification](modules/notification/page.mdx)
+- [notification-service](modules/notification_service/page.mdx)
 - [order](modules/order/page.mdx)
 - [order-models](modules/order_models/page.mdx)
 - [payment](modules/payment/page.mdx)