Configure region_name_for_services in heat.conf

backport: rocky

Not including this means that SoftwareDeployments do not have a
configured region (it's set to 'null'), and can therefore not
communicate back to the heat API. In particular, this breaks Magnum with
the following error in the journal on the deployed servers:

publicURL endpoint for orchestration service in null region not found

Change-Id: Ia2c18ef10727391812368c958262a92385374ace
Co-Authored-By: John Garbutt <john@stackhpc.com>
Closes-Bug: #1817051