Network remappers should also handle host.network.* metrics

[lahsivjar]

Current network remappers only produce system.network.* metrics, however, curated UIs also require host.network.* metrics (ref). We should produce both of these metrics in the remappers.

As per ECS, there are 4 host.network metrics that needs to be produced:

1. host.network.egress.bytes
2. host.network.egress.packets
3. host.network.ingress.bytes
4. host.network.ingress.packets

Unlike system.network.* metric, the host.network.* metrics seems to be an aggregate over all network devices and are gauges.

[lahsivjar]

#16 is a PoC to get this to work. I haven't validated the correctness yet.