Use the working v2 registry API

What does this MR do and why?

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/372795

https://registry.hub.docker.com/v1/repositories/gitlab/gitlab-ee/tags returns 410 Gone.

Switching to https://registry.hub.docker.com/v2/repositories/gitlab/gitlab-ee/tags seems to work.

See https://docs.docker.com/docker-hub/api/deprecated/

How to validate locally

bundle exec gitlab-qa Test::Omnibus::UpdateFromPrevious EE 15.4.0-pre minor --no-tests

[Sep 07 2022 13:15:04 AEST (Gitlab QA)] INFO  -- Fetching docker tags from 'gitlab/gitlab-ee' registry
[Sep 07 2022 13:15:05 AEST (Gitlab QA)] INFO  -- Performing gitlab update: gitlab/gitlab-ee:15.3.3-ee.0 => gitlab/gitlab-ee:nightly (15.4.0-pre)

I'm not sure there's a way to validate in CI currently 🤔

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.