fix(appset): add cluster secret metadata to ClusterDecisionResource generator (#25498)

[mikeshng]

Fixes [ISSUE #25498]

The ClusterDecisionResourceGenerator was missing cluster secret metadata (labels and annotations) that the ClusterGenerator already provides. This PR adds fixes this issue by fetching cluster secrets and including metadata.labels.key and metadata.annotations.key params for each matched cluster, following the same pattern used by ClusterGenerator.

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.
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[mikeshng]

FYI @ch-stark

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.47%. Comparing base (7cdc0f9) to head (a4fba8e).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
applicationset/generators/duck_type.go	80.00%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #25499      +/-   ##
==========================================
+ Coverage   62.45%   62.47%   +0.01%     
==========================================
  Files         351      351              
  Lines       49490    49520      +30     
==========================================
+ Hits        30910    30936      +26     
- Misses      15621    15622       +1     
- Partials     2959     2962       +3     

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