CDAT Migration: Prepare branch for merge to `main`

[tomvothecoder]

Description

• Closes #853

Summary of Changes

• Remove CDAT dependencies from conda env .yml files
  • Affected files: conda-env/ci.yml, conda-env/dev.yml
• Update documentation to replace CDAT and CDAT-based module references to Xarray/xCDAT
  • Affected files: available-parameters.rst, install.rst, dev_guide/adding-new-diags-sets.rst
• Remove CDAT-based derivation modules (/derivations/)
  • Affected files: acme.py, default_regions.py
• Remove CDAT-based driver modules (/driver/utils/)
  • Affected files: climo.py, dataset.py, diurnal_cycle.py, general.py
• Remove CDAT-based metrics functions
  • Affected files: metrics/__init__.py
• Replace genutil.udunits module with cf_units.Unit module
  • Affected files: derivations/utils.py
• Remove old script called e3sm_diags_vars.py
• Remove deprecated plot modules from /cartopy dir and delete /cartopy dir
• Refactor _add_contour_plot() to use _get_output_dir() and remove parameter arg + update all plot modules with this change
  • Affected files are all under /plot

Todo (later)

• Remove auxiliary_tools/cdat_regression_testing dir with regression testing material, which will no longer be needed at some point

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] My changes generate no new warnings
• [x] Any dependent changes have been merged and published in downstream modules

If applicable:

• [x] New and existing unit tests pass with my changes (locally and CI/CD build)
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have noted that this is a breaking change for a major release (fix or feature that would cause existing functionality to not work as expected)