+Steps to correct Kelvin_initialization issues

[Hallberg-NOAA]

This commit takes the first steps toward correcting problems with the Kelvin initialization code, including making the OBC nudging timescale an explicit parameter and adding a number of comments identifying concerns and suggesting possible improvements with the code that is used when KELVIN_WAVE_MODE > 0. This commit includes the introduction of the new runtime parameter KELVIN_WAVE_VEL_NUDGING_TIMESCALE, with a default value set to recover the current hard-coded answers. A new warning message cautions about the suspected problems with the internal wave version of the code. By default, all answers are bitwise identical in the 4 Kelvin wave test cases that can be found at github.com/ESMG/ESMG-configs, but there is a new parameter in the MOM_parameter_doc.all files these cases.

[Hallberg-NOAA]

@kshedstrom, because you originally contributed the user/Kelvin_initialization.F90 code, I would greatly appreciate it if you could examine these changes at your convenience to ensure that you agree with them, and in particular with the comments I have added about the internal Kelvin wave cases and how they might be fixed.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 38.10%. Comparing base (3b3fb5e) to head (6f7d22c).
Report is 5 commits behind head on dev/gfdl.

Files with missing lines	Patch %	Lines
src/user/Kelvin_initialization.F90	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           dev/gfdl     #839      +/-   ##
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- Coverage     38.11%   38.10%   -0.01%     
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  Files           298      298              
  Lines         87641    87652      +11     
  Branches      16417    16422       +5     
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+ Hits          33400    33404       +4     
- Misses        48223    48225       +2     
- Partials       6018     6023       +5     

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[kshedstrom]

I approve these changes. Thank you for looking into this problem and providing excellent suggestions in the comments.

[kshedstrom]

The squared amplitude must be a copy-paste error from the Rossby soliton. Yikes.
The factor of 0.001 is indeed problematic and without it, the case actually looks sensible for the first time.
The eta_anom idea is interesting and something that would doubtless clean up the solution. I recall that we are setting outside e to match inside e somewhere in the code. Do you happen to know where that happens? Is there any other circumstance in which we'd have a clue how to set eta_anom?