[release-1.11] Update istio gateway from v1alpha3 to v1beta1 (#1628)

[houshengbo]

cherry-pick of 5e2d097

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (b675338) 79.23% compared to head (c3749a9) 79.20%.

Files	Patch %	Lines
pkg/reconciler/knativeserving/ingress/istio.go	75.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.11    #1650      +/-   ##
================================================
- Coverage         79.23%   79.20%   -0.03%     
================================================
  Files                41       41              
  Lines              1830     1842      +12     
================================================
+ Hits               1450     1459       +9     
- Misses              276      278       +2     
- Partials            104      105       +1     

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[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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