feat: Add fileSelector to the GitFileGenerator to support label-based file match(https://github.com/argoproj/argo-cd/issues/17673)(Alpha)

[Sriteja-Tadakaluru]

Description:
This is to support more granularity on selecting files over git repositories based on the key-value pairs along with the path. This is similar to how matchLabels or matchExpressions works on kubernetes metadata objects.

Optional Field: fileSelector can be used with matchLabels/matchExpressions.

• Supports matchLabels

• Supports matchExpressions:

• For more operators(IN/EXISTS....etc)
  

• Note: This is only for the objects(doesn't work for arrays of objects).

Example CR:

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: test-fileselector
  namespace: argocd
spec:
  generators:
    - git:
        requeueAfterSeconds: 600
        repoURL: https://github.com/example-test/example.git
        revision: HEAD
        files:
          - path: testing/values-*.yaml   ====> path to the values files
            fileLabelSelector:  =========> labels/expressions used to select files.
              matchLabels:
                clusterName: test-kubernetes
                labels.env: prod
              matchExpressions:
              - key: labels.env
                operator: In
                values:
                - test1
               -  prod
                - prod1
                - prod2
  template:
    metadata:
      namespace: argocd
      name: 'test-{{Name}}'
    spec:
      project: default
      source:
        helm:
          ignoreMissingValueFiles: true
          valueFiles:
            - 'values-{{Name}}.yaml'
        path: testing
        repoURL: https://github.com/example-test/example.git
        targetRevision: HEAD
      destination:
        server: https://kubernetes.default.svc
      syncPolicy:
        automated:
          selfHeal: true

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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[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 6 lines in your changes missing coverage. Please review.

Project coverage is 55.20%. Comparing base (12a4dab) to head (0acf034).
Report is 16 commits behind head on master.

Files with missing lines	Patch %	Lines
applicationset/generators/git.go	77.77%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21281      +/-   ##
==========================================
+ Coverage   53.34%   55.20%   +1.85%     
==========================================
  Files         337      337              
  Lines       57056    57082      +26     
==========================================
+ Hits        30439    31510    +1071     
+ Misses      23974    22869    -1105     
- Partials     2643     2703      +60     

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[andrii-korotkov-verkada]

Maybe name it FileLabelSelector to be more clear it's a label selector?

[Sriteja-Tadakaluru]

Done

[reggie-k]

Thanks for the PR! Could you add documentation for this functionality?

[Sriteja-Tadakaluru]

Done, documentation has been added, Thanks!!!