Add support for percentage based request mirroring

[bjee19]

Proposed changes

Add support for percentage based request mirroring by supporting the percent and fraction fields in the HTTPRequestMirrorFilter API.

Problem: Users would like to enable percentage based request mirroring.

Solution: Add support for the percent and fraction fields in the HTTPRequestMirrorFilter API.

Testing: Added unit tests, updated conformance tests run, manually ran these test cases:

• Single HTTPRoute with single filter
• Single HTTPRoute with two filters to separate backends (one is the same backend as specified on HTTPRoute)
• Single HTTPRoute with two filters targeting same backend, higher percentage wins
• Single HTTPRoute with two filters targeting same backend, higher percentage wins (higher percentage is 100, so no split clients is made)
• Single HTTPRoute with two filters on separate RULES -- two split clients and internal locations are made even if they target the same backend
• Two HTTPRoutes with single filter create separate split clients and locations.
• 0 percentage works, same with fraction

Closes #3314

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.

Add support for percentage based request mirroring.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.06%. Comparing base (fc0a5a7) to head (2aba5c9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3627      +/-   ##
==========================================
+ Coverage   86.91%   87.06%   +0.14%     
==========================================
  Files         127      127              
  Lines       15287    15471     +184     
  Branches       62       62              
==========================================
+ Hits        13287    13470     +183     
  Misses       1847     1847              
- Partials      153      154       +1     

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[sarthyparty]

reviewing is harder than I thought

[sjberman]

Nice work!

[salonichf5]

lgtm 🚀