Add esnowanl to enkfgfs cycle

[TravisElless-NOAA]

Description

Previously the esnowanl task was setup to run only for the enkfgdas cycle. This PR adds the capability for this task to run for the enkfgfs cycle, incorporating the rotating background directory structure used by other enkfgfs tasks.

Resolves #3276

Type of change

• New feature (adds functionality)

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

How has this been tested?

3-4 cycles of an ATM with JEDI snow da experiment on Hera.
COMROOT: /scratch2/NCEPDEV/stmp3/Travis.J.Elless/comrot/test_snow_ec
EXPDIR: /scratch1/NCEPDEV/da/Travis.J.Elless/exp/test_snow_ec

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
• I have commented my code, particularly in hard-to-understand areas
• I have documented my code, including function, input, and output descriptions
• My changes generate no new warnings
• 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

[TravisElless-NOAA]

Since I don't have the ability to request additional reviewers, feel free to look at this as well @CoryMartin-NOAA

[aerorahul]

just some minor suggestions, but looks ok to me.

[jiaruidong2017]

Looks good to me. Thanks Travis for your efforts.

[aerorahul]

lgtm