Fix queries for Sentry Kube dashboard

Dashboard preview: https://dashboards.gitlab.net/dashboard/snapshot/fLzM9F6ZmVr31MYI6scaj22OvC4rBdCB

The Clickhouse-related panels on the Sentry Kube dashboard were looking at the metrics coming from the Opstrace Clickhouse cluster 🤦 I've corrected those, removed a panel showing metrics that aren't really useful to us and made the rest of the queries more specific to prevent this from happening again.