update 'standard_name' for each var in write_pp_catalog

[jtmims]

Description
@aradhakrishnanGFDL noticed an issue where all of the entries in the pp_catalog had the same name. This PR adds an update to the dict passed to make the catalog for the 'standard_name' of each variable.

Associated issue #672

How Has This Been Tested?
Ran for MJO_suite and Wheeler_Kiladis on the workstation with some GFDL data.

Checklist:

• My branch is up-to-date with the NOAA-GFDL main branch, and all merge conflicts are resolved
• The scripts are written in Python 3.12 or above (preferred; required if funded by a CPO grant), NCL, or R
• All of my scripts are in the diagnostics/[POD short name] subdirectory, and include a main_driver script, template html, and settings.jsonc file
• I have made corresponding changes to the documentation in the POD's doc/ subdirectory
• I have requested that the framework developers add packages required by my POD to the python3, NCL, or R environment yaml file if necessary, and my environment builds with conda_env_setup.sh
• I have added any necessary data to input_data/obs_data/[pod short name] and/or input_data/model/[pod short name]
• My code is portable; it uses MDTF environment variables, and does not contain hard-coded file or directory paths
• I have provided the code to generate digested data files from raw data files
• Each digested data file generated by the script contains numerical data (no figures), and is 3 GB or less in size
• I have included copies of the figures generated by the POD in the pull request
• The repository contains no extra test scripts or data files