Add config keyword for PRIORITIZE_PRIVATE_IP_ADDRESS
This commit adds the new config keyword `PRIORITIZE_PRIVATE_IP_ADDRESS`,
letting the user specify in their config/site_config if Ert should
communicate with the fm_dispatch event reporter over the host's public
or private IP address. If this setting is incorrect, the event reporter
will not be able to reach Ert, and no granular forward model step
updates will be available in the GUI.