Add proxy-set-headers annotation for ingress

[AlexFenlon]

Proposed changes

This adds the nginx.org/proxy-set-headers annotation to ingress.
As shown in option 1 in the issue, It can be used to set a custom header by setting the annotation by doing nginx.org/proxy-set-headers: "X-Forwarded-ABC"

It can also allow multiple headers by doing nginx.org/proxy-set-headers: "X-Forwarded-ABC,ABC2"

It also allows the user to set a custom value in the annotation by doing nginx.org/proxy-set-headers: "X-Forwarded-ABC: test"

It can be used in Minion and Master, as well in a non mergable/standard ingress.
The annotation set in minion, if it has the same header name eg. X-Forwarded-ABC, but different value, minion will override the master

If there are different headers in both master and minions, both master and the minion annotations will show up.

There are pytests and go tests for this functionality.

Resolves: #4772

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[shaun-nx]

Well done @AlexFenlon ! 👏

[jjngx]

👍🏻