With the the Systemd-based initrd, systemd-journald is doing the logging.
One of Journald's Trusted Journal Fields is `_HOSTNAME` (systemd.journal-fields(7)).
Without explicitly setting the hostname via this file or the kernel cmdline, `localhost` is used and captured in the journal.
As a result, a boot's log references multiple hostnames.
With centralized log collection this breaks filtering (more so when logs from multiple Systemd-based initrds are streaming in simultaneously.
Fixes#318907.