feat(auth): Revamp authentication setup (#7387)

* chore: Clean up authentication middlewares

* chore: Rename AuthUser to AuthIdentity

* feat: Define link between user, customer, and auth identity

* feat: Use links for auth, update auth context content

* fix: Adjust user create command with new auth setup

* fix: Make auth login more dynamic, review fixes

* fix: Change test assertions for created by

integration-tests/modules/__tests__/customer/admin/create-customer.ts

@@ -44,7 +44,7 @@ medusaIntegrationTestRunner({
             id: expect.any(String),
             first_name: "John",
             last_name: "Doe",
-            created_by: "admin_user",
+            created_by: expect.any(String),
           })
         )
       })