[Metricbeat] gcp: fields do not respect naming best practices

[endorama]

While working at #26824 I noticed that the current implementation of the gcp module for Metricbeat does not seem to align to naming conventions.

Examples:

• gcp.compute.instance.uptime.value is a value in seconds, for which sec suffix should be used
• gcp.compute.instance.firewall.dropped_bytes_count.value is a bytes value, for which bytes suffix should be used

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[endorama]

After reading through the code I learnt that ECS fields are exported:

beats/x-pack/metricbeat/module/gcp/metrics/metricset.go

Lines 334 to 348 in 86004dd

	hostFieldTable := map[string]string{
	"instance.cpu.utilization.value": "host.cpu.usage",
	"instance.network.sent_bytes_count.value": "host.network.ingress.bytes",
	"instance.network.received_bytes_count.value": "host.network.egress.bytes",
	"instance.network.sent_packets_count.value": "host.network.ingress.packets",
	"instance.network.received_packets_count.value": "host.network.egress.packets",
	"instance.disk.read_bytes_count.value": "host.disk.read.bytes",
	"instance.disk.write_bytes_count.value": "host.disk.write.bytes",
	}
	for _, singleEvent := range groupedEvents {
	if hostMetricName, ok := hostFieldTable[singleEvent.Key]; ok {
	hostRootFields.Put(hostMetricName, singleEvent.Value)
	}
	}

Still Beats naming conventions are not respected.