Description of problem: 

Azure Container Registry (ACR) Plugin gives 401, with a change in backstage 1.28 if proxy credentials are required

See Backstage 1.28 release notes about the BREAKING: Proxy backend plugin protected by default

• https://github.com/backstage/backstage/releases/tag/v1.28.0

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1. Install and configure ACR plugin as mentioned here https://github.com/janus-idp/backstage-plugins/blob/main/plugins/acr/README.md 

Actual results:

User will see 401, workaround is to add below in app-config

backend:
  auth:
     dangerouslyDisableDefaultAuthPolicy: true

Expected results:

Should be able to the list and should not get 401

Reproducibility (Always/Intermittent/Only Once):

Build Details:

Additional info (Such as Logs, Screenshots, etc):