Docs: Fix link in security.md

[nginx-aoife]

Broken link found in kubernetes-ingress by Docs Nightly Automation Testing

Fixing a broken link to WAFv5 docs.

• Typo in newly added link in KIC docs here https://docs.nginx.com/nginx-ingress-controller/configuration/security#configure-root-filesystem-as-read-only
• Actual: https://docs.nginx.com/nginx-app-protect-waf-v5/
• Expected: https://docs.nginx.com/nginx-app-protect-waf/v5/

Also making the "incompatible link" more specific to v4 to avoid confusion. Previously it was bringing user to top level WAF which included v4 & v5.

Please Merge and Cherry Pick into release branch if approved.

Checklist

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• 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