fix(gitops-engine): apply HideSecretData to server-side diff results for Secrets

[pjiang-dev]

Fixes #25260

Summary

Fixes Secret resources showing persistent OutOfSync status when using IncludeMutationWebhook=true with mutation webhooks.

Problem

After sync, the live Secret already contains the webhook-mutated value. On the next server-side diff, Argo CD performs dry-run SSA, which also runs the webhook and produces predictedLive. Logically, predictedLive should match live. But for core Secrets, the webhook-mutated data can differ at the raw comparison level between the dry-run result and the actual live object. Argo CD compares those bytes and marks the resource OutOfSync.

Solution

Use HideSecretData during ServerSideDiff to ensure after mutating webhook modifies secret that data is symmetrical before comparison if secret values are identical

Checklist:

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.59%. Comparing base (7c582df) to head (691eb89).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
gitops-engine/pkg/diff/diff.go	66.66%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #27598      +/-   ##
==========================================
- Coverage   63.65%   63.59%   -0.07%     
==========================================
  Files         417      417              
  Lines       57079    57134      +55     
==========================================
  Hits        36336    36336              
- Misses      17353    17402      +49     
- Partials     3390     3396       +6     

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[agaudreault]

LGTM