NGINX: reduce controller replica default to 2

What does this MR do?

NGINX: reduce controller replica default to 2

Reduce the replicas of controller and default backend to - 2 controller pods - 1 default backend

Observed during load testing of 10k reference architecture, 3 pods were capable of keeping up with all traffic. So 2 should easily handle lower than that.

Related issues

See

• #598 (comment 441187016)
• #2235 (closed)
• https://docs.gitlab.com/ee/administration/reference_architectures/

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• [ ] Tests added
• [ ] Integration tests added to GitLab QA
• [ ] Equivalent MR/issue for omnibus-gitlab opened

Closes #598 (closed)

cc @mnielsen