NewService sets up a new validator monitor service instance when given a list of validator indices to track.

AggregateReportingPeriod defines the number of epochs between aggregate reports.

Service is the main structure that tracks validators and reports logs and metrics of their performances throughout their lifetime.

ValidatorAggregatedPerformance keeps track of the accumulated performance of the tracked validator since start of monitor service.

ValidatorLatestPerformance keeps track of the latest participation of the validator.

ValidatorMonitorConfig contains the list of validator indices that the monitor service tracks, and the event feed notifier that the monitor needs to subscribe.