Add support for OCSP

[aledbf]

What this PR does / why we need it:

TODO:

• skip ocsp for default backend with fake certificate
• skip for self-signed certificates?
• use a cache to avoid unnecessary requests
  (without this we could get rate-limited and also introduces ~20s in the response time)
• lua test
• e2e test
• check if ocsp setting is enabled
• check sni host is a valid hostname for the ingress controller
• support for OCSP must staple extension?

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #4758

Special notes for your reviewer:

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf

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[codecov-io]

Codecov Report

Merging #4868 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4868   +/-   ##
=======================================
  Coverage   58.49%   58.49%           
=======================================
  Files          88       88           
  Lines        6719     6719           
=======================================
  Hits         3930     3930           
  Misses       2361     2361           
  Partials      428      428

Impacted Files	Coverage Δ
internal/ingress/controller/template/configmap.go	77.4% <ø> (ø)	⬆️

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[aledbf]

This PR is working, just need to finish pending items

[aledbf]

manual test:
openssl s_client -connect HOSTNAME:443 -servername HOSTNAME -status < /dev/null

[aledbf]

/hold

[aledbf]

/test all

[aledbf]

/retest

[k8s-ci-robot]

@aledbf: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-ingress-nginx-test-lua	088066c	link	/test pull-ingress-nginx-test-lua

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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