fix: argocd notification controller app client permission issue (cherry-pick #16057)

[gcp-cherry-pick-bot]

Cherry-picked fix: argocd notification controller app cluster permission issue (#16057)

• if applicationNamespaces is not provided as input parameter, then use namespaced appClient

Signed-off-by: May Zhang may_zhang@intuit.com

• fix go lint error

Signed-off-by: May Zhang may_zhang@intuit.com

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Signed-off-by: May Zhang may_zhang@intuit.com

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (67e1e04) 49.97% compared to head (ab333f9) 49.98%.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-2.9   #16159      +/-   ##
===============================================
+ Coverage        49.97%   49.98%   +0.01%     
===============================================
  Files              266      266              
  Lines            46065    46070       +5     
===============================================
+ Hits             23021    23029       +8     
+ Misses           20784    20782       -2     
+ Partials          2260     2259       -1     

Files	Coverage Δ
notification_controller/controller/controller.go	62.14% <100.00%> (+1.40%)	⬆️

... and 2 files with indirect coverage changes

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