UI clean-ups on cluster health charts
As part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10245, there are a few UI clean-ups that need to be made as part of a separate issue/MR.
- Adding tick marks to the chart
- Updating the formatting of the popover
- Improving the responsiveness of the popover
Further details are in: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10245#note_152627267 and https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10245#note_152997658
Edited by 🤖 GitLab Bot 🤖