Enable MPI in Ascent build

Background

The MR !2638 (merged) introduces a new CI build that runs at the OLCF Ascent (A scaled down cluster replicating OLCF summit).

MPI is currently disabled since it had issues with its job scheduler (SLURM), with enough tweaking it should be working.

Completion criteria

Add one more build that test VTKm in ascent with MPI.