Release the Docker Hub credentials support in the Dependency Proxy

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/183020



Merged-by: Dzmitry (Dima) Meshcharakou <12459192-dmeshcharakou@users.noreply.gitlab.com>
Approved-by: João Pereira <jpereira@gitlab.com>
Approved-by: Lysanne Pinto <lpinto@gitlab.com>
Approved-by: Dzmitry (Dima) Meshcharakou <12459192-dmeshcharakou@users.noreply.gitlab.com>
Reviewed-by: David Fernandez <dfernandez@gitlab.com>
Reviewed-by: João Pereira <jpereira@gitlab.com>
Reviewed-by: Dzmitry (Dima) Meshcharakou <12459192-dmeshcharakou@users.noreply.gitlab.com>
Reviewed-by: Lysanne Pinto <lpinto@gitlab.com>
Co-authored-by: David Fernandez <dfernandez@gitlab.com>