Validate duplicate panel groups in monitoring dashboard and surface a message

Problem to solve

As of %12.10, the monitoring dashboard yml files can have duplicate panel group titles and there is no validation. Features like annotations rely on the uniqueness of group titles. This issue is to display a warning message either by validating on the backend or frontend

Background

Based on #208868 (comment 310655818), it was identified that having unique panel group titles is necessary for annotations.