Add migration skipped reasons to registry dash
What does this MR do and why:
This MR adds a metric in the Migration Detail dashboard displaying the skipped import reasons and re-organizes the section it is in to fit properly.
Test dashboard: https://dashboards.gitlab.net/dashboard/snapshot/5DfSOv7AD4FHluSPjjprPlMDDjNZOeza
Edited by Steve Abrams