feat: Enhance DAU Metrics Tracking Logic for Argo CD

[leehosu]

Fixes #20801

Refactored DAU metrics logic to improve accuracy, performance, and reliability in tracking daily active users for Argo CD.

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[bot]]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 54.97%. Comparing base (83953fe) to head (c4f5b5b). Report is 40 commits behind head on master.

Files with missing lines	Patch %	Lines
server/metrics/metrics.go	33.33%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #20839 +/- ## ========================================== - Coverage 55.06% 54.97% -0.10% ========================================== Files 324 324 Lines 55397 55469 +72 ========================================== - Hits 30505 30493 -12 - Misses 22272 22353 +81 - Partials 2620 2623 +3 ```

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