fix: don't write files if secret values unchanged

[ThirdEyeSqueegee]

Issue #, if available:
N/A

Description of changes:
There is a bug in writeFile which causes it to write secret files unconditionally every poll interval regardless of whether a secret has been rotated/updated. This breaks applications which use file watchers to execute logic when the mounted secret file is modified.

The bug manifests when the rotation reconciler is enabled.

• Fix the bug: check file content before writing

Validated e2e, no unnecessary rewrites when secret value unchanged:

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.72%. Comparing base (072ee2d) to head (cb8142d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #557      +/-   ##
==========================================
+ Coverage   61.56%   61.72%   +0.15%     
==========================================
  Files          11       11              
  Lines         752      755       +3     
==========================================
+ Hits          463      466       +3     
  Misses        274      274              
  Partials       15       15              

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