Lazy load artifacts dropdown on pipeline list page

What does this MR do?

Related to #324003 (closed)

To improve performance on the pipelines list page, we are lazy loading the downloadable artifacts for each pipeline when the user clicks on the dropdown to view them.

The artifacts are still currently being loaded in this merge request, so the lazy load will technically be the second time we receive them. However, this allows us to remove the artifacts from the backend endpoint without breaking the page.

Screenshots (strongly suggested)

Lazy loading in action

Screen_Cast_2021-04-22_at_10.54.39_AM

When there is an error loading the artifacts

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done