fluids: Add PyTorch external DD SGS evaluation

[jrwrigh]

Add PyTorch as a external DD SGS evaluation. This is a "follow up" to #1361 where we use PyTorch to run the data-driven model instead of a native implementation.

ToDos:

• [x] Add in PetscLogEvents (particularly for inference and the data transfer steps)
• [x] Add documentation
• [x] Cleanup the Makefile additions (remove the automatic USE_LIBTORCH testing)
• [x] Add weak symbols so that this can be compiled without pytorch
• [x] Add command line switch to enable pytorch vs internal sequential
• [x] Move createPyTorchModel into the testing directory (it's only useful for documenting the creation of the testing model (instead of it just being a binary blob).
• [x] Rename "sequential_internal" to "sequential_ceed"

[jrwrigh]

This is good for review now. Tests pass on Noether for CPU and CUDA. I'm having some difficulties getting PyTorch+ROCM to build with Spack, but that's not a huge priority since we don't have hardware to run that on right now.