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 (85025e1) 50.03% compared to head (2cc2687) 50.03%.

Additional details and impacted files

@@             Coverage Diff              @@
##           release-2.8   #16160   +/-   ##
============================================
  Coverage        50.03%   50.03%           
============================================
  Files              263      263           
  Lines            45137    45142    +5     
============================================
+ Hits             22583    22588    +5     
  Misses           20344    20344           
  Partials          2210     2210           

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

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