Remove empty elements from comma-separated list

[WalterKolczynski-NOAA]

Description

Updates the list parsing in Configuration to remove empty strings from the comma-separated list. This will allow creating a single-element list by appending a , after the element, as well as just relax syntax on lists by ignore a trailing ,.

Refs: NOAA-EMC/global-workflow#2795

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

• [x] pynorms
• [x] pytests

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] My changes need updates to the documentation. I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] New and existing tests pass with my changes
• [x] Any dependent changes have been merged and published

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 50.12%. Comparing base (264e8f3) to head (7174ac4).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #40 +/- ## ======================================== Coverage 50.12% 50.12% ======================================== Files 18 18 Lines 1652 1652 Branches 339 339 ======================================== Hits 828 828 Misses 765 765 Partials 59 59 ```

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