Warn repo admins if they mistakenly leave useProxies set to false

useProxies is a dspace.cfg variable where an admin can indicate if DSpace is running behind a proxy or not.

When not set, the value defaults to false. This has the consequence that X-Forward-For headers will be ignored when looking for the IP that triggers the pageview or download:

https://github.com/DSpace/DSpace/blob/master/dspace-api/src/main/java/org/dspace/statistics/SolrLogger.java#L300

These IPs are vital for determining the location of the usage event.

We have come across cases where admins forget to switch the value to "true" when they move DSpace behind a proxy. If they leave this undiscovered, they are effectively registering usage events without IPs, which makes it impossible to get the location information or to do IP based bot filtering.

As an easy fix, I suggest to switch the value to true by default, because even if DSpace is NOT behind a proxy, behaviour will still be appropriate since the X-Forward-For headers won't be used if there's empty.