Add ability to ignore submodules in diff and status

TL;DR This release adds a new field to components.yaml, ignore_submodules which when true will ignore submodules in the mepo status and mepo diff calls.

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A mepo oddity occurs in GEOSgcm because of how CICE and icepack are handled.

Technically, icepack is a submodule of CICE in the repo (see https://github.com/GEOS-ESM/CICE) and git sees it as that. However, currently GEOS handles icepack as a separate repo (most likely for ease of development) but git doesn't really know this. So when you go to CICE in GEOS in a fresh clone you see:

$ git status
HEAD detached at geos/v0.0.2
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   icepack (new commits)

Submodules changed but not updated:

* icepack 81a7628...8d80ff5 (1):
  > Merge pull request #1 from GEOS-ESM/bugfix/zhaobin74/recompute-enthalpy

no changes added to commit (use "git add" and/or "git commit -a")

and since mepo status just sort of "echoes" status output with mepo status we see:

cice6                  | (t) geos/v0.0.2 (DH)
   | icepack: modified, not staged

So git says "something changed" but we want to ignore that in this case.

Thus, this PR adds a new field to components.yaml, ignore_submodules:

cice6:
  local: ./src/Components/@GEOSgcm_GridComp/GEOSogcm_GridComp/GEOSseaice_GridComp/CICE_GEOSPlug/@cice6
  remote: ../CICE.git
  tag: geos/v0.0.2
  develop: geos/develop
  ignore_submodules: true

If this is true, then we add --ignore-submodules=all to underlying git calls when we run mepo diff and mepo status

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From CHANGELOG.md

Added

• Added new ignore_submodules field in components.yaml to allow ignoring submodules in a repo. Currently used for status and
  diff commands.

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What's Changed

• Add ability to ignore submodules by @mathomp4 in #258
• GitFlow: Merge Develop into main by @mathomp4 in #259

Full Changelog: v1.50.0...v1.51.0