Allow defining the default keymap to be used by
vconsole-setup through a build option. A template
vconsole.conf also gets populated by tmpfiles if
it doesn't exist.
This adds /etc/locale.conf to the set of configuration files
populated by tmpfiles.d factory /etc handling.
In particular, the build-time locale configuration in systemd is
now wired to a /usr factory file, and installed to the system.
On boot, if other locale customization tools did not write
/etc/locale.conf on the system, the factory default file gets
copied to /etc by systemd-tmpfiles.
This is done in order to avoid skews between different system
components when no locale settings are configured. At that point,
systemd can safely act as the fallback owner of /etc/locale.conf.
This mirrors what was done in 564761fcae
for sysusers.d. If we allow separating resolved sysusers config
in a subpackage, we should do the same for the symlink that is
only useful when resolved is installed.
Related to #21317.
HAVE_SMACK_RUN_LABEL was dropped back in 348b44372f,
so one line in etc.conf was not rendered as expected ;(
Checking if names are defined is paying for itself!
