Revert to using a hostname for the druid_public services

We had attempted to switch away from a hostname to a load-balanced endpoint for the druid_public data purge jobs.

However, this did not work for the initial data purge job because we do not yet have the druid coordinator and overlord services under LVS. It is only the druid-broker service that is load-balanced.

For now, we will revert to using a hostname, but we will look at whether we can use LVS for the other druid services, as well.

Bug: T403955