GitHub Issue NOAA-EMC/GSI#417. Add continuous integration build tests for Intel and GNU compilers.

[aerorahul]

This PR:

• adds 2 github actions CI files .github/workflows/gcc.yml and .github/workflows/intel.yml. These actions build the GSI, EnKF and the utilities using the GCC and Intel compiler suite respectively.
• The suites are built and cached to be used in subsequent builds thus saving time and resources.
• The suites and dependencies are built using Spack
• The dependencies are stored in ci/spack.yaml

Closes #417

Once merged, one can track the Actions for e.g see the push action for this PR at https://github.com/aerorahul/GSI/actions

[MichaelLueken]

@aerorahul - I'm fine with moving forward with this update. However, you will need to reduce the number of commits from 12 to 1 and ensure that you add NOAA-EMC#417 to the final commit message. You can do these by:

• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git commit --amend
• Please add NOAA-EMC#417 at this point.
• git push origin feature/ci --force

[aerorahul]

@aerorahul - I'm fine with moving forward with this update. However, you will need to reduce the number of commits from 12 to 1 and ensure that you add NOAA-EMC#417 to the final commit message. You can do these by:

• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git reset --soft HEAD~1
• git commit --amend
• Please add NOAA-EMC#417 at this point.
• git push origin feature/ci --force

done.

[MichaelLueken]

@aerorahul Thanks! I will now move forward with adding continuous integration build test for Intel and GNU compilers to the authoritative repository.

[MichaelLueken]

Since there are no changes to the source code and do not affect results, I will give final approval to these changes and merge them to the authoritative develop branch.