When installing IPA server in certain environments like containers, some defaults might need to be different, while giving the admin a way to modify them for their particular deployment. There should be a defaults file where the packager/vendor would set the generic defaults, and admin should be able to override the default in both ways.

Take the NTP as an example -- it's defined in the code

    basic_group.add_option("-N", "--no-ntp", dest="conf_ntp", action="store_false",
                      help="do not configure ntp", default=True)

so the user can disable it. But what if we want to have it disabled as a general rule for containerized deployment, while giving the admin a chance to actually enable it? We'd need to come up with some extra parameters specific to invocation of the container (docker run command taking some environment variables, for example), rather than just configuring that the default is {{{--no-ntp}}} and giving the admin standard way, to override it back, like {{{--enable-ntp}}}.

Similar behaviour should be possible for all boolean options of all installers.