WIP: Insights change to dropdown

❗ Based off of insights-multi-charts-per-page https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10516

Above MR changes insights to per page rather than per chart. https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10516 should be merged first

What does this MR do?

Changes the insights tabbed selector to a dropdown

• This will accommodate any number of pages without overflowing
• Adheres better to the guidelines in the design guide
  • https://design.gitlab.com/components/dropdowns/

What are the relevant issue numbers?

TODO

• Regenerate individual chart images for Docs
• Regenerate overall insights images for Docs

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer