Build Nodes Overview dashboard

[estolfo]

Build the Nodes Overview dashboard using the Logstash metrics exported via OTLP.

[estolfo]

[estolfo]

Differences between the existing Nodes Overview dashboard and the OTel one:

1. Load Average — the column is gone entirely from the table. The metric is metrics.logstash.os.cpu.load_average.1m in the existing integration but it's a flow rate metric and there's no non-flow rate value we can use there.

Added Load Average to table in 74a93f835362b765275d36674ef46c6ba977c2f1