Add Singularity.omb-5.8-ubuntu-18.04-cuda-11.2-mlnx-ofed-4.7-3.2.9.0-openmpi-4.0.5

Another OMB container (and its base container layers) built to assist
with testing CUDA-enabled OpenMPI to help investigate a problem with
multi-GPU node support in Expanse's software deployment. Again, these
containers will also be used to prepare acceptance tests on Expanse for
the upcoming deployment of Voyager.