adding BackendTimeout for Gateway API router

[dkulchinsky]

adding service.backendTimeout for Gateway API router that maps to HTTPRouteTimeouts.BackendRequest, this complements the existing service.timeout setting that maps to HTTPRouteTimeouts.Request

[aryan9600]

left a small nit, but lgtm otherwise - thanks! 🙇

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 30.00%. Comparing base (cd964bb) to head (61582f7).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/router/gateway_api.go	76.47%	4 Missing ⚠️
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1920      +/-   ##
==========================================
- Coverage   30.18%   30.00%   -0.19%     
==========================================
  Files         288      288              
  Lines       18533    18455      -78     
==========================================
- Hits         5594     5537      -57     
+ Misses      12204    12189      -15     
+ Partials      735      729       -6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.