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__/users/get-me.spec.ts

@@ -27,7 +27,7 @@ medusaIntegrationTestRunner({
 
         expect(response.status).toEqual(200)
         expect(response.data).toEqual({
-          user: expect.objectContaining({ id: "admin_user" }),
+          user: expect.objectContaining({ id: expect.any(String) }),
         })
       })
     })