Move some configuration logic from Nginx config to Lua code

[ElvinEfendi]

What this PR does / why we need it:

• use Lua code to do some conditional variable assignments instead of Nginx's map directive
• move HTTP to HTTPs redirection logic to Lua

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #3790

Special notes for your reviewer:

[aledbf]

@ElvinEfendi please no. Migrating to lua will reduce the number of users that can customize the configuration. I think we need to rethink the map part but no in this way

[ElvinEfendi]

If you ask me Lua code is easier to understand (also easier to test) than that complicated maps and ifs we do in the configuration. I'll leave this here to sink a bit, maybe we will reconsider :)

And we can simplify the hell out of the existing Lua code - it was done in under 5m, literally translated the maps into Lua code.

[aledbf]

I change my last comment because we keep seeing use cases that are not possible to support using map and if. For that reason, I think this could be a good idea to at least try.

[aledbf]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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