Add new grafana dashboard for sign-in metrics
Test dashboard: https://dashboards.gitlab.net/dashboard/snapshot/dsiVv0mZGqhEqZ7uQ1u7CcFj6KW8T5jG?orgId=1
Add a new dashboard to track possible changes in sign-ins before and after implementing the Arkose captcha
Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/355746
Edited by Andras Herczeg