fix: (call .repo.GetAppDetails).Helm is Null for multi-sources applications

[aryasoni98]

Description

Fixes #26760

For multi-source Argo CD applications, (call .repo.GetAppDetails) in notification templates always returned nil for Helm, so Helm values (e.g. image.tag) could not be read via $appDetails.Helm.GetParameterValueByName. The function always used source index 0, which for multi-source apps is often the values repo, not the Helm chart.

This change adds an optional source index argument so callers can specify which source to inspect (e.g. (call .repo.GetAppDetails 1) for the second source). It also passes RefSources for multi-source apps so $values references in Helm value files resolve correctly.

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Checklist:

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[ppapapetrou76]

Consider adding UTs especially for edge cases

[nitishfy]

Left some nits, PTAL!

[codecov]

Codecov Report

❌ Patch coverage is 78.12500% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.98%. Comparing base (6df1a5b) to head (aa2be31).

Files with missing lines	Patch %	Lines
util/notification/argocd/service.go	46.15%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #26773      +/-   ##
==========================================
+ Coverage   62.97%   62.98%   +0.01%     
==========================================
  Files         414      414              
  Lines       56154    56180      +26     
==========================================
+ Hits        35362    35386      +24     
  Misses      17420    17420              
- Partials     3372     3374       +2     

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[nitishfy]

Please fix the lint checks.