release/1.5.1: fix py-pandas/py-openpyxl version incompatibility, fix ectrans variants mkl/fftw

[climbfuji]

Description

This time I am doing it the other way round, add to release/1.5.1 and then merge back to develop by cherry-picking the commits ...

1. Fix Version conflict of py-pandas and py-openpyxl spack-stack#818 by adding the required version of py-openpyxl and the version requirement in py-pandas.
2. Fix Intel CI container build failed in ectrans spack-stack#820 by explicitly asking for mkl (which itself is a virtual provider) or fftw (which is a package) instead of fftw-api (which is a virtual provider and can be fftw or mkl). We'll likely want to redo some of this in a cleaner way when we work on Switch to Intel MKL on systems with Intel compiler spack-stack#759 in the future.

For testing, see JCSDA/spack-stack#821

Issue(s) addressed

Resolves JCSDA/spack-stack#818
Resolves JCSDA/spack-stack#820

Dependencies

n/a

Impact

None

Checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have run the unit tests before creating the PR

[climbfuji]

I know from the spack PRs that there will be updates to these commits, but for release/1.5.1 this is good enough. I will try to cherry-pick the changes in this PR, then apply the updates from spack develop, when I merge this back to jcsda_emc_spack_stack.