Build Node Overview Advanced dashboard

[estolfo]

Build the Node Overview Advanced dashboard using the Logstash metrics exported via OTLP.

[estolfo]

[estolfo]

Differences between this dashboard and the existing one:

1. System Load chart — is excluded as the metric is a flow rate metric and there's no OTel equivalent
2. OS-wide CPU % — not in the Logstash metric store; the existing integration computes it on-demand via ProcessMonitor.java's getSystemCpuLoad() when the REST API is called. Could be added by calling ProcessMonitor directly from otel.rb
3. Node Summary table: Default Pipeline Workers / Default Batch Size — node-level concepts that don't map cleanly to OTel, which tracks these per-pipeline only