Add initial zone_sync values to the ConfigMap

[AlexFenlon]

Proposed changes

This pr adds the following zone_sync values to the default nginx-config ConfigMap.

• zone-sync true/false
• zone-sync-port - int

zone-sync-port requires zone-sync to be enabled, which in turn needs NGINX Plus enabled.

Domain is also added and is written dynamically based on the namespace of the controller eg.
nginx-ingress-headless.nginx-ingress.svc.cluster.local

This PR only just adds the values and the validation for it, the user cannot enter anyhing until future implementation.
Resolves: #7218

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-config
  namespace: nginx-ingress
data:
  zone-sync: true
  zone-sync-port: 1234

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

[codecov]

Codecov Report

Attention: Patch coverage is 62.79070% with 16 lines in your changes missing coverage. Please review.

Project coverage is 52.72%. Comparing base (4dbfc2e) to head (46838e2).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/configs/configmaps.go	62.79%	11 Missing and 5 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7239   +/-   ##
=======================================
  Coverage   52.72%   52.72%           
=======================================
  Files          89       89           
  Lines       20843    20886   +43     
=======================================
+ Hits        10989    11012   +23     
- Misses       9396     9409   +13     
- Partials      458      465    +7     

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