Missing `host_hostname` field in Collector receiver messages

~All messages from the file log receiver type are missing the `host_hostname` field. The field is present in the journald and windowseventlog messages.~

We should add a `host.name` [resource attribute](https://opentelemetry.io/docs/specs/semconv/registry/attributes/host/) to each OTel message via a processor. (similar to how we add the `collector.` resource attributes.

That way we get a consistent hostname for all log messages and don't have to rely on data from the log message itself.

For the own-logs of the supervisor and collector we have to set the programmatically because we can't configure their pipeline in YAML.