fix: run server as nonroot with non-read-root-fs

[sbose78]

• Mount /home/argocd for plugins' usage
• Split from fix: run argo-cd repo server as non-root with read-only-root-fs #5814 to isolate risks.
• part of Add readOnlyRootFilesystem to securityContext #3648

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.
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[sbose78]

don't feel too comfortable mounting /home/argocd as emptydir: {}

[codecov]

Codecov Report

Merging #5820 (d76139f) into master (84f0594) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5820      +/-   ##
==========================================
- Coverage   41.02%   41.00%   -0.02%     
==========================================
  Files         146      146              
  Lines       19616    19630      +14     
==========================================
+ Hits         8047     8049       +2     
- Misses      10455    10466      +11     
- Partials     1114     1115       +1     

Impacted Files	Coverage Δ
util/settings/settings.go	39.46% <0.00%> (-0.48%)	⬇️
cmd/argocd/commands/app.go	0.00% <0.00%> (ø)
pkg/apis/application/v1alpha1/types.go	57.44% <0.00%> (+0.23%)	⬆️

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[alexmt]

LGTM