[exporter/datadog] Incorrect preview hostname on GKE

[mx-psi]

Describe the bug

The hostname on Google Kubernetes Engine when using the exporter.datadog.hostname.preview feature gate should be the same as in Google Cloud Engine VMs, but it is the Kubernetes hostname. This causes the hostname to not match the one reported by other Datadog products in Google Cloud.

Steps to reproduce

Run the OpenTelemetry Collector with the Datadog exporter on a GKE cluster.

What did you expect to see?

The hostname should be <instance hostname>.<cloud account id>.

What did you see instead?

The hostname is <node name>.<cluster name>.

What version did you use?

v0.54.0