Add search domain list to the group_vars/prod to override the default we used during development.

The search domain list we use during development is aimed at our adhoc cluster Bright CoD.

We need a way to define the search domain list for production deployment, we can do this by adding these values via group_vars/prod. The deploy time var ENV in the .gitlab-ci.yml script will assign the host to ansible group prod, so ansible knows to use group_vars/prod for prod related values that will override the defaults.