Added weighted_v3 with sidekiq weight.

Contributes to gitlab-com/gl-infra/scalability#2326 (closed)

This will start the recording of an SLA labeled weighted_v3 that includes Sidekiq at a weight of 1. This will make the version selectable from the SLA dashboard https://dashboards.gitlab.net/d/general-slas/general-slas?orgId=1. We can make that the default by changing the template (https://gitlab.com/gitlab-com/runbooks/blob/bf6e2ed91c313b316078ec5ab4d8f384305065db/libsonnet/grafana/templates.libsonnet#L228) after we get approval.