Resolve "Monitoring graphs - Popover value improvements"

What does this MR do?

Adds the popover values improvements and the circle to the hover line

Screenshots (if relevant)

The canary bug, solved

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #41783 (closed), https://gitlab.com/gitlab-org/gitlab-ee/issues/5573

EE counterpart:

https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5458 no conflicts it just so happens the only way to test canary is on EE, the frontend code is shared between two versions