Adding new files for github actions testing of spack package

[G-Ragghianti]

Using this PR to test new spack package test. Don't merge yet.

[G-Ragghianti]

I tested this on my fork, and it appears that the github interface requires that this spack.yml file is merged into master before we will be able to run tests manually. Therefore, I will temporarily set this to run on PRs (so that the spack tests will run in this PR), and I'll temporarily disable the other CI actions in main.yml (just for this PR) so that we don't waste resources running the automatic checks.

After we are confident that the spack test are running as desired, we should set the spack.yml to only run manually and the main.yml tests back to running automatically.

[G-Ragghianti]

@mgates3 The pre-installation tests (make check) both in the cmake and spack build report skipped: requires num_devices > 0 for the gpu_amd device tests. Do you know why this would be?

[mgates3]

The test_norm unit test didn't see the GPU devices due to a minor issue in the run_tests.py script, which was setting (CUDA|ROCR)_VISIBLE_DEVICES='' for test_lq. It's safe to ignore. I'll submit a work around.

[mgates3]

The issue with test_norm skipped: requires num_devices > 0 should be now resolved by #187. See the 2 unit_test commits; sorry those are unrelated to the shared library version which was the PR's main topic, they just got rolled into it.

[G-Ragghianti]

This can be merged