Initial YAML configuration support

[jkrasting]

Description

• Framework will attempt to read supplied configuration
  files as YAML format first, then falls back to JSON if needed
• Change should be backward-compatible with existing .jsonc files
• Added a new parse_serialization_stream function and private
  _parse_yaml function
• Renamed existing parse_json to a private _parse_json
• Updated doc references and unittests

Associated issue # (replace this phrase and parentheses with the issue number)

How Has This Been Tested?
Sample NOAA_GFDL user config supplied in YAML format

Checklist:

• [x ] I have reviewed my own code to ensure that if follows the POD development guidelines
• [x ] My branch is up-to-date with the NOAA-GFDL develop branch, and all merge conflicts are resolved
• [ x] The script are written in Python 3.6 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
• If applicable, I've added a .yml file to src/conda, 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
• The repository contains no extra test scripts or data files