cli/command: RegistryAuthenticationPrivilegedFunc: fix hints for login

[thaJeztah]

• relates to docker pull is now interactive moby/moby#50204
• relates to cli/command: Reapply "remove uses of GetAuthConfigKey, ParseRepositoryInfo" and add test #5969

The RegistryAuthenticationPrivilegedFunc has some conditional logic to add additional hints when logging in to the default (Docker Hub) registry. Commit 9f4165c inadvertently passed the wrong variable to PromptUserForCredentials, which caused it to show the additional hints for Docker Hub.

Before this patch, hints were printed for the default (docker hub) registry;

docker pull icr.io/my-ns/my-image:latest

Login prior to pull:
Log in with your Docker ID or email address to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com/ to create one.
You can log in with your password or a Personal Access Token (PAT). Using a limited-scope PAT grants better security and is required for organizations using SSO. Learn more at https://docs.docker.com/go/access-tokens/

Username:

With this patch, those hints are omitted;

docker pull icr.io/my-ns/my-image:latest

Login prior to pull:
Username:

- What I did

- How I did it

- How to verify it

- Human readable description for the release notes

Fix a regression where a login prompt on `docker pull` would show Docker Hub-specific hints when logging in on other registries.

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

I want to look at improving these messages overall, as a the "Login prior to pull:" is a bit awkward, and nothing in the output indicates what registry it's prompting for.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 55.04%. Comparing base (f53bb88) to head (e2632c5).

❌ Your patch status has failed because the patch coverage (0.00%) is below the target coverage (50.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6135   +/-   ##
=======================================
  Coverage   55.04%   55.04%           
=======================================
  Files         361      361           
  Lines       30152    30152           
=======================================
  Hits        16596    16596           
  Misses      12598    12598           
  Partials      958      958           

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