R21C HISTORY output specs (precip, land, landice, ...)

[gmao-rreichle]

This PR proposes updated R21C HISTORY specs on top of @sdrabenh's R21C branch.
See also matching PR #356 in GEOSgcm_App
These updates will eventually need to find their way into the default and/or FP file specs in the 'develop' branch, which will require another PR.

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Details:

Updates are focused on (but not entirely limited to) land and landice outputs.

For land outputs in the "lnd" collection, appended/inserted "LAND" in LONG_NAME wherever there's any chance at all that users could be confused that the output is only over land tiles.

Clarified LONG_NAME for volumetric soil moisture (m3/m3) vs dimensionless soil wetness.

Made variables that are exported in R21C consistent across land and landice (incl. runoff).

Fixed sign issue for GHTSKIN in landice.

Still to do:

1. Figure out how to deal with LONG_NAME of model vs. corrected precipitation. In MERRA-2, the words "bias corrected" were appended somehow to LONG_NAME for PRECTOTLAND and PRECSNOLAND.
   a. "Bias corrected" is not a good term; going forward, we should use "observation corrected" because the corrections are applied at the daily scale.
   b. Adding "observation corrected" to the LONG_NAME in *GridComp.F90 files requires thought because currently the F90 files supports both uncorrected and corrected precip over land in the same export variable.

2. Add runoff (and other variables?) averaged across land and landice. [DONE @lcandre2, @gmao-rreichle 16Nov22]

3. Resolve conflicting signs for GHTSKIN (GHLAND?) in landice and land collections. [DONE @lcandre2 16Nov22]

4. Resolve assorted in-line comments (to be added). [DONE @gmao-rreichle 17Nov22]

I'll keep working on this, but please feel free take a look and add your 2c.

For precip outputs, figure out how to clarify model vs. corrected in the LONG_NAME.

cc: @elakkraoui @lcandre2 @gmao-qliu @lltakacs @sdrabenh @rcullath @rdkoster @rlucches

[lcandre2]

My changes from /feature/lcandre2/r21c_landice_changes are now incorporated fully in this branch.

1. long_name changes to RUNOFF from SURFACE and LANDICE (and other children of SURFACE to maintain consistency).

There is still one outstanding issue. 'RUNOFF' exported from 'SURFACE' in the flx collection should provide combined runoff from land and landice. However, a test indicated that the entire grid are no data values. 'RUNOFF' from LANDICE exports correctly, so the details of how this export propagates up through to SURFACE from LAND, LANDICE, & LAKE are beyond me. So, I am tagging @elakkraoui @sdrabenh @lltakacs

[gmao-rreichle]

Many thanks, @sdrabenh, for merging this PR.
I double-checked that everything that was in the branch was merged ok, so I'm going to delete my branch. For any future changes that may be needed, we'll start with another clone of your most recent branch.
I'll also transfer the remaining to-do items into a new Github issue #683.
cc: @elakkraoui @lcandre2