docs: customer tiers tutorial (#14122)

* docs: customer tiers tutorial

* fix lint error

www/apps/resources/generated/generated-tools-sidebar.mjs

@@ -829,6 +829,14 @@ const generatedgeneratedToolsSidebarSidebar = {
                   "title": "Create Order Returns",
                   "children": []
                 },
+                {
+                  "loaded": true,
+                  "isPathHref": true,
+                  "type": "ref",
+                  "title": "Customer Tiers",
+                  "path": "https://docs.medusajs.com/resources/how-to-tutorials/tutorials/customer-tiers",
+                  "children": []
+                },
                 {
                   "loaded": true,
                   "isPathHref": true,