allow to configure jaeger header names

[mkabischev]

What this PR does / why we need it:

This PR allows to configure jaeger header names as mentioned in https://github.com/opentracing-contrib/nginx-opentracing#getting-started

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[mkabischev]

/assign @bowei

[aledbf]

/ok-to-test

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@846ff00). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #4569   +/-   ##
=========================================
  Coverage          ?   59.38%           
=========================================
  Files             ?       89           
  Lines             ?     6848           
  Branches          ?        0           
=========================================
  Hits              ?     4067           
  Misses            ?     2343           
  Partials          ?      438

Impacted Files	Coverage Δ
internal/ingress/controller/config/config.go	97.16% <ø> (ø)
internal/ingress/controller/nginx.go	29.44% <ø> (ø)

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[aledbf]

/lgtm

[aledbf]

@mkabischev thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, mkabischev

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