config: prefer configuration specified files

config: prefer configuration specified files

Suricata-Update was preferring the existence of "disable.conf" in
$sysconfdir over it be specified in the update.yaml.

Refactor the auto-conf to only search and apply the default
$sysconfdir files if they don't already exist in the config.

Additonally, now that the default, if not set or found will be none,
log a warning if a specific configuration file is not found instead of
silently ignoring.

Ticket: #6172