Adding simple tool to make unstructured grids for E3SM

Description:

This adds a python script and xml file that can be used to subset an existing domain/surface file into an unstructured vector of grid-cells for E3SM. This may work for a single cell run with CTSM, but is untested.

Collaborators:

Expectation of Answer Changes:

Checklist

If this is your first time contributing, please read the CONTRIBUTING document.

All checklist items must be checked to enable merging this pull request:

Contributor

[ ] The in-code documentation has been updated with descriptive comments
[ ] The documentation has been assessed to determine if updates are necessary

Integrator

[ ] FATES PASS/FAIL regression tests were run
[ ] Evaluation of test results for answer changes was performed and results provided

Documentation

Technical Note update:
User's Guide update:

Test Results:

CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag:

FATES baseline hash-tag:

Test Output:

NGEET / fates