Add mean remediation time in the Security Dashboard

Problem to solve

Security Dashboard shows information about vulnerabilities, but there is no data about how fixing vulnerabilities is doing.

We want to track vulnerabilities and how much time it takes to fix them. We could present this information in the dashboard.

Proposal

Add the mean resolution time for issues in the dashboard. It should be specific for each severity, so we know how much time it takes to fix, for example, a Critical problem. We can reuse the same summary or add some new element.

We can also show average and 95% so there are clear numbers to benchmark against.

Depends on: First Class Vulnerabilities