[Libbeat] Move adding host.name into add_host_metadata

[kaiyan-sheng]

Currently we have libbeat adding host.name before the global add_host_metadata processor is executed:
https://github.com/elastic/beats/blob/master/libbeat/publisher/processing/default.go#L337

We should move adding host.name into add_host_metadata in the future. Each module should also add their own host.name fields instead relying on add_host_metadata processor if possible.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.