feat(translator): combine services across httproutes expression router

[randmonkey]

What this PR does / why we need it:

Second part of #5801. Generate combined Kong services for rules sharing the same bakends when expression based routes are used.

Which issue this PR fixes:

Fixes #6727

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Attention: Patch coverage is 86.36364% with 9 lines in your changes missing coverage. Please review.

Project coverage is 79.0%. Comparing base (4f6373f) to head (5eb89d1).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...al/dataplane/translator/subtranslator/httproute.go	83.3%	4 Missing and 2 partials ⚠️
...ataplane/translator/subtranslator/httproute_atc.go	89.6%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6766     +/-   ##
=======================================
+ Coverage   77.7%   79.0%   +1.2%     
=======================================
  Files        208     208             
  Lines      24833   24766     -67     
=======================================
+ Hits       19314   19579    +265     
+ Misses      4539    4191    -348     
- Partials     980     996     +16     

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