Add CEL tests for `NginxProxy` Policy

[shaun-nx]

Overview

As a user of NGF, I would like to add CEL tests for the NginxPolicy CRD so that I can be confident that the CEL validation works as I expect

UACs

• Add test for the kubernetes CEL validation
• Add test for the rewriteClientIP CEL validation

kubernetes validation:

x-kubernetes-validations:
  - message: only one of deployment or daemonSet can be set
    rule: (!has(self.deployment) && !has(self.daemonSet)) || ((has(self.deployment)
      && !has(self.daemonSet)) || (!has(self.deployment) && has(self.daemonSet)))

rewriteClientIP validation:

x-kubernetes-validations:
  - message: if mode is set, trustedAddresses is a required field
    rule: '!(has(self.mode) && (!has(self.trustedAddresses) || size(self.trustedAddresses)
      == 0))'

[nginx-bot]

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