Support condor_ssh_to_jpb also for Singularity jobs
This requires HTCondor to invoke singularity [#20811] and [#21875]
At the moment this works only for privileged HTCondor installations
Glidiens start HTCondor as an unprivileged user
There are some testing and troubleshooting to do to make sure that this works for unprivileged HTCondor. This will be in collaboration w/ the HTCondor team.