Improve copy making it more clear what "Last updated" means in the Container Registry UI

Context

This issue arises after a discussion on Slack where a customer raised confusion over what "Last updated" meant in the Container Registry UI:

It's also not clear how Last updated and Published relate:

The "Last updated" in the UI is showing the updated_at field in the rails record for the associated ContainerRepository object, so it's the last time that object was modified.

Many things can cause updated_at at to change, including:

• cleanup running
• cleanup policies changing
• container repository was migrated

Problem

• It's not clear what last updated means
• Many of the things that update "last updated" happen outside of this UI, so customers could be looking to the UI to tell them what was updated and they will not see anything obvious

Proposed solution

Show created_at instead of updated_at in this field:

Implementation guide

• In https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/packages_and_registries/container_registry/explorer/components/details_page/details_header.vue#L68-73
  • Refactor timeAgo computed property to use createdAt
  • Refactor updatedText computed property to be createdText
• Remove updatedAt from GraphQL request