Add OOM-kills and cgroup runbook link to cgroup row on Gitaly host dashboard

Added OOM-kills and link to cgroup runbook for gitaly to cgroups row, to correlate OOM kills with cgroup resource usage more easily.

Link to the test dashboard: https://dashboards.gitlab.net/dashboard/snapshot/ts4Yv141K7Tnj0fHyuqVBgJT4055T9fM?orgId=1