Laghos: in container

We need a reproducer for building a container on one machine (e.g., an LC machine), and running it on another machine (e.g., AWS).

- [ ] What type of a container? Docker?
- [ ] Is it possible to build a `container` version of a package? If yes, we could use Spack to build the container.
- [ ] Running is difficult, particularly if file systems are in play - at the very least, we have to store the caliper files etc.

Study performance difference on communication cost of how you build the container wrt MPI.
- [ ] Hybrid method: install MPI in the container. Compile the code with MPI X, ideally the same implementation as on AWS.
- [ ] Host MPI: bind in MPI when you build it, bind another MPI when run on AWS.

No files or tests are named. Start by resolving the container format, Spack packaging approach, and MPI strategy for building on an LC machine and running on AWS. Done means a reproducible container workflow that preserves required Caliper files and measures communication-cost differences between hybrid and host-MPI approaches.

Written by the indexing model from the issue text.