The current implementation from Journald input translates _HOSTNAME to host.hostname: https://github.com/elastic/beats/blob/367d94e1dc40a82713d651735eac7921bb584474/filebeat/input/journald/pkg/journalfield/default.go#L57C3-L57C12

However our documentation states that _HOSTNAME is translated to host.name.

We need to make our documentation and implementation match as well as clarify the difference between those two fields.