[release-1.15] preserve appropriate header matches when creating the virtualservice

[knative-prow-robot]

This is an automated cherry-pick of #1349

Properly propagate route header matching rules to the virtual service

[ReToCode]

/lgtm
/approve

[knative-prow]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.19%. Comparing base (a8bc624) to head (ef761ce).

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.15    #1350      +/-   ##
================================================
- Coverage         82.20%   82.19%   -0.02%     
================================================
  Files                25       25              
  Lines              1602     1601       -1     
================================================
- Hits               1317     1316       -1     
  Misses              189      189              
  Partials             96       96              

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