Run conformance tests in pod on cluster

[ciarams87]

Proposed changes

Problem: The conformance tests send traffic to the IPs of the NKG Pod for the corresponding Gateway. However, all tests that send traffic are failing with:

http.go:217: Request failed, not ready yet: Get "http://<POD-IP>": dial tcp <POD-IP>80: i/o timeout (after 26µs)
and

http.go:217: Request failed, not ready yet: Get "http://<POD-IP>/": context deadline exceeded (after 22.3µs)

This is because we are running the tests in a Docker container on the local machine which cannot access the internal pod network.

Solution: Instead of running the tests in a Docker container, run the tests in a pod on the cluster. This also includes configuring RBAC for the appropriate CRUD access to the required resources. Additionally, the Makefile commands have been updated to preload the NGINX image to the local cluster, and to remove the requirement to manually edit the deployment manifests with the image under test.

Note: This PR adds a requirement for the utility yq to be installed locally - see https://github.com/mikefarah/yq.

Testing: Ran all commands locally. Tests are now passing traffic successfully.

Closes #771

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

[pleshakov]

a few nits and consistency comments. otherwise, looks good!