add admission control functionality

[aburan28]

What type of PR is this?
This adds the admission control filter.
Exposes the the configuration on the backendtrafficpolicy crd

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What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Release Notes: Yes/No

[codecov]

Codecov Report

❌ Patch coverage is 38.41060% with 93 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.10%. Comparing base (3c310a2) to head (03d92f3).

Files with missing lines	Patch %	Lines
internal/xds/translator/admission_control.go	40.17%	57 Missing and 10 partials ⚠️
internal/gatewayapi/backendtrafficpolicy.go	7.40%	24 Missing and 1 partial ⚠️
internal/xds/translator/httpfilters.go	91.66%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (38.41%) is below the target coverage (60.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7529      +/-   ##
==========================================
- Coverage   72.28%   72.10%   -0.18%     
==========================================
  Files         231      232       +1     
  Lines       34084    34225     +141     
==========================================
+ Hits        24637    24678      +41     
- Misses       7673     7760      +87     
- Partials     1774     1787      +13     

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[zhaohuabing]

A bool field with a default of true is a little counter-intuitive. Would it make sense to flip the flag and call it PassThrough? Or maybe we could drop it for the firt iteration.

[arkodg]

hey @aburan28 you've also raised #7016 for adding adaptive concurrency control support, these are similar options to throttle clients based on server characteristics ( latency, load), would help if you can outline your use case first, so we can prioritize one or the other, and document the reasons for adding support for it