The lines stored in `extraConfig` and `worker.<name?>.extraConfig`
should take precedent over values from included files but in order to do
this in rspamd UCL they need to be stored in a file that then gets
included with a high priority. This commit uses the overrides option to
store the value of the two `extraConfig` options in `extra-config.inc`
and `worker-<name?>.inc` respectively.