fix: Application controller can run out of disk space on '/dev/shm' (#19201)

[jgwest]

Closes #19201

This PR allow the user to customize which path with the application controller container is used to store temporary kubernetes manifests.

See parent issue, and gitops-engine issue/PR, for details.

This PR:

• Application controller now reads manifest generation path from ARGOCD_APPLICATION_CONTROLLER_MANIFEST_GENERATION_PATH
  • application controller startup command updated
  • Application controller Deployment/StatefulSet updated to optionally read the value from argocd-cmd-params-cm
• One can customize this path via controller.manifest.generation.path in argocd-cmd-params-cm
  • I've likewise updated the argocd-cmd-params-cm docs
• Integrates with changes made in gitops-engine PR, to allow the customization of manifest gen path: Enable consumers of gitops-engine API to specify an alternative temp directory for generated manifests, as an alternative '/dev/shm' gitops-engine#613
  • Any location in the code that was using the old behaviour (use '/dev/shm') will continue to use the old behaviour.
  • This includes unit test and git repo https creds in util/git/creds.go

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).
• The title of the PR conforms to the Toolchain Guide
• 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.
• 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).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

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[jgwest]

Note to self/reviewer: Ensure this is removed after gitops-engine PR is merged.

[codecov]

Codecov Report

Attention: Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 55.87%. Comparing base (9af0ff5) to head (cbbf2bb).

Files	Patch %	Lines
util/git/creds.go	60.00%	2 Missing ⚠️
cmd/argocd/commands/admin/app.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #19202   +/-   ##
=======================================
  Coverage   55.87%   55.87%           
=======================================
  Files         316      316           
  Lines       43794    43798    +4     
=======================================
+ Hits        24471    24474    +3     
  Misses      16775    16775           
- Partials     2548     2549    +1     

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