Fix binding to multiple listeners with empty section name

[kate-osborn]

Proposed Changes

A refactor of the route binding logic done in #633 introduced a bug with empty section name. This PR fixes that bug.

Problem: If an HTTPRoute has a parentRef with an empty section name, and the referenced gateway has multiple valid listeners, the route would only bind to the first listener.

Solution: Attempt to bind to every valid listener in the referenced Gateway.

Testing: Added a unit test that reproduced the issue and manually verified that a route with empty section name can attach to multiple valid listeners.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork