Add apptainer support

Closes #694

[ x] Defined the tests that specify a complete and functioning change (It may help to create a design specification & test specification)
[x ] Implemented the source code change that satisfies the tests
[ x] Documented the feature by providing worked example
[x ] Updated the README or other documentation
[ x] Completed the pre-Request checklist below

Change Description

add apptainer definition file, README, and update CMakeLists.txt so code compiles
closes #694
didn't try to add xios
probably don't need all the python libraries installed in the image (@timspainNERSC, you could perhaps suggest a minimal list for compilation)

cmake works in apptainer container (can now find the correct python in that case). The container is ubuntu 22.04.
model runs and produces output

[x ] The requirements of this pull request are fully captured in an issue or design specification and are linked and summarised in the description of this PR
[ x] No new warnings are generated
[ x] The documentation has been updated (or an issue has been created to track the corresponding change)
[ x] Methods and Tests are commented such that they can be understood without having to obtain additional context
[ x] This PR/Issue is labelled as a bug/feature/enhancement/breaking change
[ x] File dates have been updated to reflect modification date
[ x] This change conforms to the conventions described in the README