Prometheus has many modes for CPU usage metrics and we only share information
about few of them. We recently hit a case where softirq usage was significant
(> 10%), but it was not shown in the dashboard, because it was not one of the
metrics we were showing in the dashboard.
This commit adds softirq usage to the dashboard, so that we can see it in the
future. It seems it is interesting enough to be shown in the dashboard.
49118add77