[VSA] Tidy up chart titles

Problem

VSA's chart titles are messy and clutter up the page. They also push the charts further down the page which hinders discoverability.

Proposal

1. Add key metrics above metrics for clarity (covered by #359060 (closed))
2. Hide "The average time spent in the selected stage for the items that were completed on each date. Data limited to the last 500 items." behind a tooltip for Days to completion
3. Remove type of work title and append "Showing data for group 'GitLab.org' from Dec 9, 2021 to Jan 7, 2022" to description below.
4. Hide Tasks by type description behind a tooltip.

Implementation guide

• Remove the type of work heading
• Move this description into a tooltip next to the Tasks by type heading

Note: We could probably move the tasks by type heading into the type of work component as a minor refactor too