feat(repo): add support for github app authentication without installationid (#25339)

[pbhatnagar-oss]

Issue: https://github.com/argoproj/argo-cd/issues/25339

Checklist:

• [x] 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).
• [x] The title of the PR conforms to the Title of the PR
• [ ] 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.
• [x] 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).

[bunnyshell[bot]]

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[codecov[bot]]

Codecov Report

:x: Patch coverage is 45.45455% with 90 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 62.53%. Comparing base (df2a759) to head (27bc003). :warning: Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
util/git/creds.go	65.26%	19 Missing and 14 partials :warning:
...licationset/services/internal/github_app/client.go	0.00%	26 Missing :warning:
pkg/apis/application/v1alpha1/repository_types.go	15.78%	15 Missing and 1 partial :warning:
cmd/argocd/commands/admin/repo.go	0.00%	6 Missing :warning:
applicationset/generators/pull_request.go	0.00%	2 Missing :warning:
applicationset/generators/scm_provider.go	0.00%	2 Missing :warning:
applicationset/services/pull_request/github_app.go	0.00%	2 Missing :warning:
applicationset/services/scm_provider/github_app.go	0.00%	2 Missing :warning:
cmd/util/repo.go	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #25374      +/-   ##
==========================================
- Coverage   62.58%   62.53%   -0.05%     
==========================================
  Files         353      353              
  Lines       49871    50002     +131     
==========================================
+ Hits        31213    31271      +58     
- Misses      15670    15723      +53     
- Partials     2988     3008      +20     

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[FourFifthsCode]

Tested functionality and working ok with github app and source hydrator without installation ID 🚀