[release-1.22] Limit the webhook request body size

[knative-prow-robot]

This is an automated cherry-pick of #3362

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.88%. Comparing base (2279959) to head (d143718).
⚠️ Report is 1 commits behind head on release-1.22.

Additional details and impacted files

@@              Coverage Diff              @@
##           release-1.22    #3363   +/-   ##
=============================================
  Coverage         74.87%   74.88%           
=============================================
  Files               189      189           
  Lines              8347     8349    +2     
=============================================
+ Hits               6250     6252    +2     
  Misses             1853     1853           
  Partials            244      244           

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[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, knative-prow-robot

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