feat: add NetworkPolicy template

[GabboPenna]

Proposed changes

This PR adds optional NetworkPolicy support to the nginx-ingress Helm chart. It introduces:

• A new networkPolicy section in values.yaml:
  • Enable/disable flag (enabled)
  • Configurable policyTypes (Ingress/Egress)
  • podSelector, ingress and egress rule definitions
• A new template charts/nginx-ingress/templates/controller-networkpolicy.yaml that renders a Kubernetes NetworkPolicy resource when networkPolicy.enabled = true

With this change, chart consumers can declare fine‑grained network controls for their Ingress controller pods without external manifests.

If this PR addresses a GitHub issue, please replace the placeholder below with the real issue link.
Fixes: #

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 feature works
• I have checked that all unit tests pass after adding my changes (helm lint .)
• I have updated necessary documentation (e.g. README, values comments)
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my fork’s branch
• I have hereby read the F5 CLA and agree to its terms

[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
_{Posted by the CLA Assistant Lite bot.}

[GabboPenna]

I have hereby read the F5 CLA and agree to its terms

[AlexFenlon]

Hi @GabboPenna,

Thanks for this PR,

Can you please create an issue for this so we can track it appropriately.

[GabboPenna]

Hi @GabboPenna,

Thanks for this PR,

Can you please create an issue for this so we can track it appropriately.

Hi @AlexFenlon, i open a new issue: #8060