feat: Support ExternalName Services

[ciarams87]

Proposed changes

Problem: NGF does not support routing to services outside the cluster

Solution: Add support for ExternalName type Services.

Testing: Tested locally targeting httpbin.org for both HTTPRoute and TLSRoute

Closes #243

Checklist

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• 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

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

Added support for ExternalName Service

[codecov]

Codecov Report

❌ Patch coverage is 97.59036% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.00%. Comparing base (5688ba8) to head (b5c2241).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/controller/nginx/config/upstreams.go	83.33%	2 Missing and 1 partial ⚠️
internal/controller/state/dataplane/convert.go	66.66%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3759      +/-   ##
==========================================
+ Coverage   86.87%   87.00%   +0.13%     
==========================================
  Files         128      128              
  Lines       16202    16404     +202     
  Branches       62       62              
==========================================
+ Hits        14075    14273     +198     
- Misses       1953     1956       +3     
- Partials      174      175       +1     

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[sjberman]

Can I make one small request to be added in this PR? Though irrelevant, I don't think it warrants a brand new PR.

In the servers nginx template, right after js_preload_object, can you add another newline? I've noticed in some rendered nginx configs, a server block renders on the same line and it looks off.

[shaun-nx]

All looks great from what I can see. Left two comments that aren't blocking the PR. Great job @ciarams87! 🎉