insights: fix query runner worker metrics

Created by: leonore

closes #39838 (closed)

the issue was that the metrics identifier name was changed, and that was actually associated to the metrics themselves. if we change the metrics name now though, we can get visibility into the past.

Test plan

locally:

sg start enterprise-codeinsights &
sg start monitoring

create some insights to trigger some queue activity

navigate to https://sourcegraph.test:3443/-/debug/grafana/d/worker/worker?orgId=1

before	after

also changing the metrics name on dogfood, for example shows this works