Update CDAT to xCDAT

[lee1043]

As the lifespan of CDAT is coming to an end, LLNL has developed xCDAT, which offers major CDAT capabilities using the xarray framework.

The CDAT library is now in maintenance-only mode, with plans for deprecation and cease of support around the end of calendar year 2023. Until this time, the dependencies for specific CDAT packages (cdms2, cdat_info, cdutil, cdtime, genutil, libcdms) will be monitored to ensure they build and install in Conda environments. CDAT currently supports Python versions 3.7, 3.8, 3.9, and 3.10. Unfortunately, feature requests and bug fixes will no longer be addressed.

With that being considered, PMP is in active to migrate to xCDAT, and such conversion is also needed for this ENSO metrics package.