Update oncall metrics dashboard (#2400)

# What this PR does
- Add new panels to OnCall Metrics dashboard with the new metric
"user_was_notified_of_alert_groups"
- Remove unused param for dashboard tab from plugin.json
- Fix old panels

## Which issue(s) this PR fixes

## Checklist

- [ ] Unit, integration, and e2e (if applicable) tests updated
- [ ] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)