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/api/__tests__/admin/api-key.spec.ts

@@ -38,7 +38,7 @@ medusaIntegrationTestRunner({
           expect.objectContaining({
             id: created.data.api_key.id,
             title: "Test Secret Key",
-            created_by: "admin_user",
+            created_by: expect.any(String),
           })
         )
         // On create we get the token in raw form so we can store it.