lorax-composer supports modifying timeservers, this stage implements it.
I was concerned if I should name this stage timeservers or chrony, but
I've decided to go with chrony. If some day in future Fedora/RHEL
changes the ntp client, we can easily introduce new stage named after
the new ntp client. Additionally, this solution enables us to create
systemd-timesyncd stage, which can change timeservers when chrony is not
installed (in that case systemd-timesyncd takes over the ntp
synchronization).