add panel for failing registrations

[xenowits]

🎯 Problem to be solved

Users don't have a way to check if their validator registrations are failing. There's also a feature currently in progress in charon that adds failing registrations as health-check.

The health check combined with the new panel will enable our users to more effectively monitor their MEV setups.

🧪 Tests

Add a panel to this repo that shows failing registrations similar to the following (Charon Overview v3/Duties):

A modification of the following prometheus query can work:

max(increase(app_eth2_errors_total{endpoint=~"submit_validator_registrations", cluster_name=~"$cluster_name"}[$__range])) by (cluster_peer, cluster_name)

👐 Additional acceptance criteria

None

❌ Out of Scope

None