Add support for custom climatology maps

[xylar]

The task ClimatologyMapCustom can be used to make climatology maps of 2D and 3D fields on cells, the latter with vertical dimension nVertLevels or nVertLevelsP1.

To support this, RemapDepthSlicesSubtask has been updated to support nVertLevelsP1 and a new utility function has been added to compute the z coordinate at layer interfaces.

Checklist

• User's Guide has been updated
• If this PR adds a new analysis task, it has also been added to the user's guide
• Developer's Guide has been updated
• API documentation in the Developer's Guide (api.rst) has any new or modified class, method and/or functions listed
• Documentation has been built locally and changes look as expected
• Testing comment in the PR documents testing used to verify the changes

[xylar]

@irenavankova, this is the first of 2 features you requested. It seems to work, see:
https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.xylar/analysis/v3.LR.piControl/clim_custom/ocean/index.html
(config options here https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.xylar/analysis/v3.LR.piControl/clim_custom/v3.LR.piControl.cfg)

(Note: the web server has cached old versions of some plots. Hopefully, these will update again in a few hours.)

I need to:

• add documentation
• test on 2D fields
• run the test suite (in progress)

In the meantime, give it a shot and let me know what you think. Happy to add more variables to defaults.cfg that you think might be useful.

[xylar]

Testing

Here are some update results showing both 2D and 3D fields, the latter with both nVertLevels and nVertLevelsP1 as the vertical dimension:
https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.xylar/analysis/v3.LR.piControl/clim_custom/ocean/index.html

I have also successfully run the developer suite:
https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.xasay-davis/analysis_testing/chrysalis/add-climatology-map-at-depths/

[xylar]

I think this will be ready for review as soon as v1.13.0 get released.