Create average age of ~bug issues chart for embedded dashboards

Objective

To provide better insight into the average age of all bug issues within a team.

Proposal

• Match the MTTC metrics in embedded Dashboard with the performance indicator from a name and style perspective.
• Split https://app.periscopedata.com/app/gitlab/809473/Temp:-Average-bug-age-exploratory?widget=10796844&udv=1225952 into two charts for severity1 and severity2
• Have one row for severity1 and severity2 metrics with an MTTC and Bug Backlog health chart
• Replace https://about.gitlab.com/handbook/engineering/quality/performance-indicators/#open-s1-and-s2-bugs with a new S1 and S2 Average Age PIs from https://app.periscopedata.com/app/gitlab/736012/Quality-Embedded-Dashboard