Support custom listener ports

[kate-osborn]

Proposed changes

Problem: NKG only supported listener ports 80 and 443. This limitation prevents the conformance tests from running because the conformance tests create a base Gateway that listens on port 8080.

Solution: Allow users to specify any port between 1-65535.

Testing:

• Added/updated unit tests to cover new code.
• Manually tested all examples using both 80/443 and 8080/8443.
• Manually verified that routes can attach to multiple listeners with the same hostname as long as they specify different ports.
• Ran conformance tests and verified that we can get past setup.

Closes #619

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

[sjberman]

Looks good, can you do a manual test where we have multiple listeners without hostnames, on different ports, and then an HTTPRoute without a section name, and verify that we properly create a server for both ports with the HTTPRoute hostname, and traffic flows through either port?

This was a case I wanted to test when I implemented the empty section name work, but couldn't due to the port restriction.

[kate-osborn]

Looks good, can you do a manual test where we have multiple listeners without hostnames, on different ports, and then an HTTPRoute without a section name, and verify that we properly create a server for both ports with the HTTPRoute hostname, and traffic flows through either port?

This was a case I wanted to test when I implemented the empty section name work, but couldn't due to the port restriction.

Yep. Verified this works with multiple http & https listeners.