Perlmutter: GPU Docker Container (#6389)

Finalize a proper, pre-build WarpX for Perlmutter GPUs with
GPU-aware/GPUdirect MPI.

## To Do

- [x] Builds
- [x] Finalize Entrypoint

# Follow-Up 

- [ ] Finalize MPI tuning based on INC0245154 response/guidance
- [ ] Ensure it runs on Perlmutter
- [ ] Ensure GPU-aware MPI/GPUdirect works
- [ ] Ensure Slingshot is used optimally (something something Cray
MPICH)
- [ ] Build all WarpX dims
- [ ] Docs

Author: ax3l