Emphasis the importance of auth registry

What does this MR do?

The container registry requires the auth config to be set up properly or users will be able to download images that they are not authorized to do so.

For example gitlab-runner#3652

What are the relevant issue numbers?

gitlab-runner#3652

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• ~~Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.~~