Add monitoring hook

[Oussema-ben-h]

This Hook replaces the values of the signals by the metrics: Rate, Delay, lost and out-of-order sequences

[stv0g]

Dear @Oussema-ben-h,

I beliefe this functionality is already present in the current version of VILLASnode.

We support using special signal expressions in the path configuration:
https://villas.fein-aachen.org/docs/node/config/paths#complex-signal-mapping-expressions

Example

paths = [
	{
		in = [
                        "udp_node.data[0-2]",
			"udp_node.hdr.sequence",
			"udp_node.hdr.length",
			"udp_node.ts.origin",
			"udp_node.ts.received",
			"udp_node.stats.owd.last",
			"udp_node.stats.skipped.total",
		],
		...
	}
]