add a switch to use either 2014-2013 mean or sliding 6 year mean MERRA2 aerosol

[AnningCheng-NOAA]

Description

add a switch to use either 2014-2013 mean or sliding 6 year mean MERRA2 aerosol. So SFS can use the sliding 6 year mean aerosol. GFS and GEFS use the 2014-2023 mean aerosol

Please use this format for your description:

Resolves [https://github.com//issues/3755
Refs #4321
Refs NOAA-EMC/repo#567](
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Type of change

• Bug fix (fixes something broken)
• New feature (adds functionality)
• Maintenance (code refactor, clean-up, new CI test, etc.)

Change characteristics

• Is this a breaking change (a change in existing functionality)? NO
• Does this change require a documentation update? NO
• Does this change require an update to any of the following submodules? NO (If YES, please add a link to any PRs that are pending.)
  • EMC verif-global
  • GDAS
  • GFS-utils
  • GSI
  • GSI-monitor
  • GSI-utils
  • UFS-utils
  • UFS-weather-model
  • wxflow

How has this been tested?

Checklist

• Any dependent changes have been merged and published
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• [X ] I have commented my code, particularly in hard-to-understand areas
• [X ] I have documented my code, including function, input, and output descriptions
• [X ] My changes generate no new warnings
• [X ] New and existing tests pass with my changes
• This change is covered by an existing CI test or a new one has been added
• Any new scripts have been added to the .github/CODEOWNERS file with owners
• I have made corresponding changes to the system documentation if necessary

[aerorahul]

@AnningCheng-NOAA
Please fix the description of this PR. The description is hidden in the comment section of the PR template.

[AnningCheng-NOAA]

@aerorahul done