Backstage - v1.26.4

This release fixes several issues related the new authentication system:

• TechDocs will now work as intended when deploying the backend using the old backend system.
• The default SignInPage will now allow guest auth even if it's not able to reach the backend.
• The TechDocs CLI now mocks the correct authentication endpoint, fixing a 404 error when previewing documentation.
• The search collators for the catalog and explore plugins will now properly authenticate requests when deployed with the new backend system.
• The JWKS endpoint used for cross-plugin authentication is now available immediately upon creation, avoiding 503 errors during startup when trying to fetch remote keys.