Displays the last published date for container repository

What does this MR do and why?

Displays the last published date for container repository.

The field was added in Expose last_published_at field from the contain... (!151506 - merged) to the GraphQL API.

This is shown in the container registry details page. lastPublishedAt field can be null from GraphQL, so this MR also handles that scenario.

Edit: Added couple of extra commits which

• Updates registry header to display images count with larger size (fixes issue mentioned in internal discussion)
• Updates details_header to conditionally fetch metadata based on metadata database enabled flag #290949 (comment 1911945594)

MR acceptance checklist

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Before	After

How to set up and validate locally

1. Setup & enable Container Registry https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/registry.md

2. Make sure to enable the metadata database https://gitlab.com/gitlab-org/container-registry/-/blob/master/docs/database-local-setup.md?ref_type=heads

3. Follow steps in https://gitlab.com/gitlab-org/ci-cd/package-stage/package/-/wikis/Packages-Tips-&-Tricks#how-to-add-images-with-tags-quickly-to-the-registry

4. Run the following in the terminal

   $ ./publish.sh <project-path> 5 1 127.0.0.1:5000 # creates 1 image with 5 tags

5. Visit the container registry tags list page in group & project view

6. Confirm that last published date is visible on the image repository details header

7. Confirm that when container registry metadata database is disabled & GITLAB_SIMULATE_SAAS is not set, last published date is not visible on the image repository,

Related to #290949 (closed)