Add CI build & unit testing

[AlexanderRichert-NOAA]

Description

Creating this issue to discuss and plan the addition of CI workflows to the repository for building and testing all code modifications.

Solution

I've added a GCC-and-MPICH-based CI workflow in my fork; currently it only builds, I have not added any tests: https://github.com/AlexanderRichert-NOAA/fv3atm/tree/develop
Here's my first successful run of the CI, which currently has two jobs, for building with 32 and 64 bit reals: https://github.com/AlexanderRichert-NOAA/fv3atm/actions/runs/7122152262

Next steps

If the CI so far looks good, then the main next step is to add unit tests with CTest. I would recommend we add a checklist to this issue to establish at least two or three initial tests, merge it into develop, then create one or more issues for adding further tests. Other possible additions we can discuss include the use of Intel, other MPI flavors, code coverage checks, and documentation (e.g., Doxygen).

[AlexanderRichert-NOAA]

@edwardhartnett @junwang-noaa

[edwardhartnett]

This is great progress. Can you put up a PR with the changes needed and the workflows?

[AlexanderRichert-NOAA]

See #730