chore: reorganize docs apps (#7228)

* reorganize docs apps

* add README

* fix directory

* add condition for old docs

www/apps/resources/app/commerce-modules/api-key/relations-to-other-modules/page.mdx

@@ -0,0 +1,19 @@
+export const metadata = {
+  title: `Relations between API Key Module and Other Modules`,
+}
+
+# {metadata.title}
+
+When Commerce Modules are used together in a Medusa application, the Medusa application handles building the relations between these modules.
+
+This document showcases the relation between the API Key Module and other Commerce Modules.
+
+## Sales Channel Module
+
+You can create a publishable API key and associate it with a sales channel. The Medusa application forms a relation between the `ApiKey` and the `SalesChannel` data models.
+
+![A diagram showcasing an example of how resources from the API Key and Sales Channel modules are linked](https://res.cloudinary.com/dza7lstvk/image/upload/v1710170465/Medusa%20Resources/api-key-sales-channel_ylpl6t.jpg)
+
+This is useful to avoid passing the sales channel's ID as a parameter of every request, and instead pass the publishable API key in the header of any request to the Store API route.
+
+Learn more about this in the [Sales Channel Module's documentation](../../sales-channel/publishable-api-keys/page.mdx).