fix: correct MaxSurge default assignment in SetDefaultDeploymentStrategy

[Xio-Shark]

Summary

Fix a bug in SetDefaultDeploymentStrategy where the default value for MaxSurge was incorrectly assigned to MaxUnavailable instead of MaxSurge.

Before (buggy):

if strategy.RollingUpdate.MaxSurge == nil {
    maxSurge := intstr.FromString("25%")
    strategy.RollingUpdate.MaxUnavailable = &maxSurge  // wrong field
}

After (fixed):

if strategy.RollingUpdate.MaxSurge == nil {
    maxSurge := intstr.FromString("25%")
    strategy.RollingUpdate.MaxSurge = &maxSurge  // correct field
}

Impact

When MaxSurge was not explicitly set, the function would:

1. Overwrite the previously set MaxUnavailable default with the maxSurge value
2. Leave MaxSurge as nil
3. This would cause the maxSurge==0 && maxUnavailable==0 fallback logic to incorrectly trigger

Test

• go build ./... passes
• go vet ./... passes

Made with Cursor

[kruise-bot]

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[kruise-bot]

Welcome @Xio-Shark! It looks like this is your first PR to openkruise/rollouts 🎉

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.38%. Comparing base (8416512) to head (c2d9d8c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #332   +/-   ##
=======================================
  Coverage   51.38%   51.38%           
=======================================
  Files          66       66           
  Lines        8559     8559           
=======================================
  Hits         4398     4398           
  Misses       3575     3575           
  Partials      586      586           

Flag	Coverage Δ
unittests	51.38% <ø> (ø)

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