fix(l1): modify Grafana dashboards so they can be filtered by instance (#4831)

**Motivation**

The Ethrex L1 Perf grafana dashboard currently doesn't let us filter by
instance, it only works as a standalone dashboard for 1 ethrex instance.

**Description**

The instance filter now has a regex to avoid having to choose from each
prometheus target: `server:port` and instead just filter by `server` and
let it choose the port according to the different metric each pane needs
to check

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Co-authored-by: Rodrigo Oliveri <[email protected]>

Author: klaus993