Docs: Change header levels of last three sections (#23587)
Docs: Change header levels of last three sections (#23587)

The last three sections of this document are not rendered on https://grafana.com/docs/grafana/latest/alerting/notifications 
It seems like in all other instances (other .md docs of this project), level one headers are only used at the top of the page, so I assume using level two headers will make them show. Level two headers do also match the overall structure of the documentation.
grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana