fix: make submodule fetching (and recursion) configurable per App (#10174)

[crenshaw-dev]

Closes #10174

TODO:

• Write unit tests (might be tricky, because the tertiary submodule needs to be inaccessible - maybe just verify that it isn't fetched?)
• Test on a live example
• Write docs

In both ListApps and GetRevisionMetadata we perform checkouts without having access to any particular app config to disable submodule recursion. Is that okay? Will the inability to block recursive fetching in those contexts break the add-app/sync-app UI workflow? Needs investigation.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• Optional. My organization is added to USERS.md.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).

[codecov]

Codecov Report

Merging #10188 (b4568b4) into master (15ac1a6) will decrease coverage by 0.00%.
The diff coverage is 34.88%.

@@            Coverage Diff             @@
##           master   #10188      +/-   ##
==========================================
- Coverage   45.92%   45.91%   -0.01%     
==========================================
  Files         227      227              
  Lines       27403    27444      +41     
==========================================
+ Hits        12584    12601      +17     
- Misses      13110    13132      +22     
- Partials     1709     1711       +2     

Impacted Files	Coverage Δ
pkg/apis/application/v1alpha1/types.go	53.29% <0.00%> (-1.42%)	⬇️
util/helm/cmd.go	25.00% <0.00%> (-0.30%)	⬇️
util/git/creds.go	40.64% <33.33%> (-0.54%)	⬇️
util/git/client.go	50.16% <54.54%> (+0.98%)	⬆️
applicationset/services/repo_service.go	57.14% <100.00%> (ø)
reposerver/repository/repository.go	64.34% <100.00%> (+0.03%)	⬆️
util/settings/settings.go	50.90% <0.00%> (ø)
...is/applicationset/v1alpha1/applicationset_types.go	34.69% <0.00%> (ø)
applicationset/generators/matrix.go	72.97% <0.00%> (+0.37%)	⬆️
applicationset/generators/merge.go	61.00% <0.00%> (+0.39%)	⬆️
... and 1 more

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[crenshaw-dev]

Closing in favor of a much simpler solution proposed by @ashutosh16: #10174 (comment)

Will reopen this if OP indicates the workaround isn't viable.