Provisional ProxySettingsPolicy proposal

[ciarams87]

Proposed changes

Problem: As a user of NGF
I want a design to configure NGINX's proxy buffer configuration for my applications through the use of ProxySettingsPolicy
So that I can implement the ProxySettingsPolicy CRD

Solution: Create the provisional ProxySettingsPolicy enhancement proposal

Partially implements #4067

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

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.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.14%. Comparing base (fc3c682) to head (9003805).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4237   +/-   ##
=======================================
  Coverage   86.13%   86.14%           
=======================================
  Files         131      131           
  Lines       14196    14196           
  Branches       35       35           
=======================================
+ Hits        12228    12229    +1     
  Misses       1765     1765           
+ Partials      203      202    -1     

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