Add `last_downloaded` date to the Package Registry UI

Context

#362259 (closed) proposes adding the last downloaded date to the Package model. This data will be helpful in step 1 of the epic &8064.

Problem to solve

Although the information will be added to the model, it still needs to be added to the user interface so that users of the Package Registry can see the last time a given package was downloaded.

Reach and impact

We have about 300k page views of the Package Registry per month. I believe adding this data point can help increase the total number of page views by 10%.

Design logic

• Only shown on the package detail page
• Follows the date and time guidelines
• Omits time, only shows the date
• If _last_downloaded returns nothing, the UI shows nothing

Design links

• Figma
• Attached ⬇

Implementation guide

• Query new field lastDownloadedAt here https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/packages_and_registries/package_registry/graphql/queries/get_package_details.query.graphql
• Add metadata-item to https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/packages_and_registries/package_registry/components/details/package_title.vue & use value from field.