Add functional tests for ClientSettingsPolicies

[kate-osborn]

Proposed changes

Problem: No automated functional tests for ClientSettingsPolicies.

Solution: Add functional tests for ClientSettingsPolicies.

Test Cases:

• NGF writes the correct status on policies
  • Valid policies are accepted
  • Conflicting policies are marked as conflicted
  • Invalid policies are not accepted
• NGF propagates the body.maxSize setting in the NGINX config. This is the only field in ClientSettingsPolicy that we can test e2e by sending traffic.

Closes #1762

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

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.