feat: Add BackendUtilization + WeightedZones support (WrrLocality Lb policy)

[jukie]

What this PR does / why we need it:
Adds the ability to use wrr_locality which is a wrapped Lb Policy of client_side_weighted_round_robin while respecting locality weights.

Which issue(s) this PR fixes:

Fixes #8635

Release Notes: No - Existing release note for BackendUtilization is sufficient. I'll follow-up after this with a docs example too.

[netlify]

✅ Deploy Preview for cerulean-figolla-1f9435 canceled.

Name	Link
🔨 Latest commit	554d63a
🔍 Latest deploy log	https://app.netlify.com/projects/cerulean-figolla-1f9435/deploys/69cc9001b5c7870008b50e87

[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.44%. Comparing base (4dcb964) to head (554d63a).

Files with missing lines	Patch %	Lines
internal/xds/translator/cluster.go	88.23%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8634      +/-   ##
==========================================
+ Coverage   74.41%   74.44%   +0.03%     
==========================================
  Files         243      243              
  Lines       38336    38363      +27     
==========================================
+ Hits        28526    28561      +35     
+ Misses       7814     7803      -11     
- Partials     1996     1999       +3     

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