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:

• [x] 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.
• [x] The title of the PR states what changed and the related issues number (used for the release note).
• [x] The title of the PR conforms to the Title of the PR
• [x] 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.
• [x] Does this PR require documentation updates?
• [x] I've updated documentation as required by this PR.
• [x] I have signed off all my commits as required by DCO
• [x] 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.
• [x] 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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[mikeshng]

FYI @ch-stark

[codecov[bot]]

Codecov Report

:x: Patch coverage is 80.00000% with 6 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 62.47%. Comparing base (7cdc0f9) to head (a4fba8e).

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

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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