fix(appset): don't emit k8s events for unchanged apps, log at debug (#15659)

[ericblackburn]

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This is a manual cherry pick for 2.9, created by request: #15660 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9075601) 50.02% compared to head (f111da9) 50.03%.

Additional details and impacted files

@@             Coverage Diff              @@
##           release-2.9   #16562   +/-   ##
============================================
  Coverage        50.02%   50.03%           
============================================
  Files              267      267           
  Lines            46196    46204    +8     
============================================
+ Hits             23111    23119    +8     
  Misses           20818    20818           
  Partials          2267     2267           

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