Initial infrastructure

[spencerkclark]

Summary of changes

This PR adds an initial working prototype of a Python wrapper of SHiELD:

• 2ab2ff8 adds initial code infrastructure for building SHiELD in a Docker container.
• 3ff32b7 copies in the code of the current fv3gfs-wrapper in the fv3gfs-fortran repository.
• 3516098 modifies this code such that we have a minimal working wrapper (with some features which rely on moderate changes to the source code of the base model left to be implemented later).
• a7db213 adds a basic CircleCI workflow for building the image and running tests within the image.

Changes required to GFDL repositories

There were some minimal changes needed to be made to a couple GFDL-owned repositories:

• An option for building a static library version of the dynamical core and drivers needed to be added to SHiELD_build (branch), as well as for building all code with the -fPIC flag (needed for building the wrapper).
• A few containers needed to be marked as public in the atmos_drivers repository (branch) -- literally a one-line change.

These were currently added by pointing the relevant submodules to the appropriate branches on forks. Before merging this PR we should propose / discuss those changes to folks at GFDL and see if we can get those merged into the main public forks first.

Important features currently removed

A few features, which we use in fv3net, were not ported immediately as they require changes to the fortran code, which I prefer to handle on a case-by-case basis. These include:

• The ability to prescribe radiative fluxes seen by the land surface model.
• The ability to transform the winds between the A and D grid from Python (note upon further inspection this actually doesn't need any updates to SHiELD, but I'll make this update to the wrapper in a separate PR since this one is already large; see this commit in a branch).
• The ability to "get" fields from the diagnostics container in the physics.
• Tests of the ability to prescribe the sea surface temperature from Python (this is handled slightly differently in the SHiELD physics driver so I want to make sure I understand that first).

[mcgibbon]

Nice job!

[spencerkclark]

NOAA-GFDL/SHiELD_build#28 and NOAA-GFDL/atmos_drivers#26 have now been merged, which enables us to pin to commits on the main branches of both of those repos (see 5885352). This PR can now be merged.