api: Added support for weighted field in BackendRef

[NayanPahuja]

What type of PR is this?
feat(api): Added support for weighted field in BackendRef

What this PR does / why we need it:

• Enabled support for weight in backendRef field, helps in traffic splitting in non x-routes.
  Which issue(s) this PR fixes:
  Fixes Support weight field for non x-routes #7449
  Release Notes: Yes

[NayanPahuja]

cc: @arkodg
Made core functional changes and tested locally.

Will need your help on what tests should I exactly write for this PR. I will make the necessary changes to the same PR.

Edit:

Also I see that since BackendRef is referenced other places such as the down below. Let me know if any subsequent changes are required since these might be impacted as well.

ALSEnvoyProxyAccessLog
BackendCluster
ExtProc
GRPCExtAuthService
HTTPExtAuthService
OIDCProvider
OpenTelemetryEnvoyProxyAccessLog
ProxyOpenTelemetrySink
RemoteJWKS
TracingProvider

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.30%. Comparing base (4784e5a) to head (7a5793e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7452      +/-   ##
==========================================
+ Coverage   72.27%   72.30%   +0.03%     
==========================================
  Files         232      232              
  Lines       34109    34114       +5     
==========================================
+ Hits        24653    24667      +14     
+ Misses       7680     7673       -7     
+ Partials     1776     1774       -2     

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[arkodg]

hey @NayanPahuja thanks for filling this gap, the code LGTM
can you also add a test case in https://github.com/envoyproxy/gateway/tree/main/internal/xds/translator/testdata to make sure IR->xDS translation exists for ext service

[arkodg]

LGTM thanks