Replace dockerfile entrypoint

[aledbf]

This changes from #3535 (comment) to:

  PID TTY      STAT   TIME COMMAND
  116 pts/0    Rs+    0:00 ps axf
    1 ?        Ss     0:00 /usr/bin/dumb-init -- /nginx-ingress-controller --def
    6 ?        Ssl    0:00 /nginx-ingress-controller --default-backend-service=i
   30 ?        S      0:00  \_ nginx: master process /usr/sbin/nginx -c /etc/ngi
   50 ?        Sl     0:00      \_ nginx: worker process
   51 ?        Sl     0:00      \_ nginx: worker process

@breunigs quay.io/kubernetes-ingress-controller/nginx-ingress-controller:dev contains this PR

Before merging this change we need to run this PR several days (to make sure we don't introduce zombie processes).
I am already doing this in several clusters. Will check on Monday if everything is working as expected

[breunigs]

As mentioned in #3535 it looks to me that this patch removes authbind from the call chain. Is that intended? I don't have a full setup here, but from a quick glance it looks like nginx still runs as www-data in this version. I would thus expect it to fail when it needs to bind low ports. I can double check that on Monday, in case quay.io/kubernetes-ingress-controller/nginx-ingress-controller:dev contains more patches that solve this differently.

[breunigs]

Please disregard my previous comment, I didn't read the ingress-nginx-controller code closely enough.

[breunigs]

I tested this and it fixes the issue described in #3533

[ElvinEfendi]

/lgtm

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