Adds a headline row for each service dashboard

Andrew Newdigaterequested to merge
an-headline-row-for-dashboard into master

Add a key service metric headline row as the first panels on every service dashboard.

image

cc @mwasilewski-gitlab

Temporary snapshot example: https://dashboards.gitlab.net/dashboard/snapshot/HYKPXV2iEKUvzgL4cm3YUmPluqcOHQXB

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