Automated CI tests

[zmoon]

Can't use the standard GHA environments since ESMF takes a long time to build, especially with MPI support. Instead, can create and use custom Docker image with ESMF already built, similar to what GEOS-Chem does. Ultimately could create a build matrix with different compilers, etc., but probably will start with Ubuntu 22.04 LTS + GFortran v11, NetCDF, etc. via apt.

Sample config with HTAP PM2.5 and PM10 only. Data files lossily compressed with NCO total ~ 500 MB. But the initial version could just check for successful NEXUS build. Then, run the sample case (Barry suggested running for 6 hours). Then, check output is consistent with reference output.