feat(translator): ext proc logs

[guydc]

What this PR does / why we need it:

This PR adds a synthetic operator %EG_EXT_FILTER_STATE(name:attribute)% that EG resolves at xDS translation time to the real %FILTER_STATE(...)% key. Users assign an optional name to each extProc entry in their EnvoyExtensionPolicy and reference it by that name in any EnvoyProxy access log format string (text or JSON). Envoy only ever sees standard operators in xDS.

Changes:

• API: Add optional Name *string field to ExtProc: the user-assigned alias for access log resolution.
• Translation: replaces %EG_EXT_FILTER_STATE(name:attr)% with %FILTER_STATE(envoy.filters.http.ext_proc/:attr)% using first-match on CustomName. Unresolved operators are replaced with "-" to prevent xDS NACK.

Which issue(s) this PR fixes:
Fixes #7868

Release Notes: Yes

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[codecov]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 73.64%. Comparing base (85e62dd) to head (619a81e).

Files with missing lines	Patch %	Lines
internal/xds/translator/listener.go	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8807      +/-   ##
==========================================
- Coverage   74.41%   73.64%   -0.77%     
==========================================
  Files         245      245              
  Lines       38977    48832    +9855     
==========================================
+ Hits        29006    35964    +6958     
- Misses       7967    10864    +2897     
  Partials     2004     2004              

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