Document deployment on-premises with no outgoing Internet connection using a Maven mirror

requested by dhanak@redhat.com follow-on to RHPAM-1282.

We now have a full description of the "no outgoing connection to the Internet" scenario for OpenShift, completed in BXMSDOC-4209. But we also need to document this scenario for on-premises. The openshift/offline-repo-proc file should probably be reused with a bit of conditioning.

viyengar@redhat.com I am not sure whom to assign to, so leaving at New and it will default to you.