Monitoring tool

[AntiD2ta]

Is your feature request related to a problem? Please describe. Along with Prometheus and Grafana features provided for every single beacon client, we could provide a monitoring tool using the Beacon Chain API, for balance and attestation check.

Describe the solution you'd like Subscribing to finalized checkpoints events, and tracking balances changes, might be enough for at least a first version of this tool. For alerting, it should be integrated for Slack, Email, Opsgenie and maybe Discord and Telegram. All of this using the Beacon Chain official API to allow integration with any consensus client.

Additional context The solution follow the approach adopted here