Pipelines graph HTML and CSS improvements and bug fixing

What does this MR do?

• Fixes all known bugs in the mini pipeline graph.
• Fixes all known bugs of dropdown with the builds, both in the mini and big pipeline graphs.
• Simplifies HTML and CSS
• Looks closer to the mockups: https://gitlab-org.gitlab.io/gitlab-design/progress/dimitrie/Object-views-issues-mr-pipelines-builds-commits/pipelines-overview/19703-spec-previews/#artboard0

Tested in following browsers:

• Mac OS Google Chrome
• Mac OS Safari
• Mac OS Firefox
• Windows Google Chrome
• Windows Edge
• Windows Firefox
• Ubuntu Google Chrome
• Ubuntu Firefox

At the moment, we have some differences between what is on master and what is on gitlab.com, see this issue description for more info - #26257 (closed)

Screenshots

Before:

After

Chrome:

Firefox:

Safari:

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #26257 (closed)