DOCS: Correct ssl-passthrough annotation description.

[r7vme]

What this PR does / why we need it:

Fixes incorrect description for nginx.ingress.kubernetes.io/ssl-passthrough annotation that was introduced by my other change.

User actually needs flag --enable-ssl-passthrough anyway if he wants to use ssl passthru. In my initial change i incorrectly assumed (and missed while testing) that only thing TCPProxy does is PROXY protocol header. Now i see that it's also does SNI. This means --enable-ssl-passthrough always required, despite PROXY protocol in load balancer.

I also created feature request to do SNI by nginx and not by ingress-controller.

My initial issue was that Go routine (with TCPProxy) crashed silently on all replicas.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): none

Special notes for your reviewer:

[aledbf]

/approve
/lgtm

[aledbf]

@r7vme thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, r7vme

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[codecov-io]

Codecov Report

Merging #2540 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2540   +/-   ##
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  Coverage   40.74%   40.74%           
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  Files          73       73           
  Lines        5021     5021           
=======================================
  Hits         2046     2046           
  Misses       2701     2701           
  Partials      274      274

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