feat: Add proxy-busy-buffers-size to NIC

[AlexFenlon]

Proposed changes

• Add -enable-directive-autoadjust flag to enable this feature
• Add proxy-busy-buffers-size to ConfigMap
• Add nginx.org/proxy-busy-buffers-size to Ingress Annotations
• Add busy-buffers-size to VirtualServer
• Add a page that tells users what exactly the new auto adjust feature does.
• Update Ingress-nginx shared annotations to include nginx.org/proxy-busy-buffers-size

NIC PR: nginx/kubernetes-ingress#8133

Checklist

Before sharing this pull request, I completed the following checklist:

• I read the Contributing guidelines
• My branch adheres to the Git conventions
• My content changes adhere to the F5 NGINX Documentation style guide
• If my changes involve potentially sensitive information¹, I have assessed the possible impact
• I have waited to ensure my changes pass tests, and addressed any discovered issues

Footnotes

1. Potentially sensitive information includes personally identify information (PII), authentication credentials, and live URLs. Refer to the style guide for guidance about placeholder content. ↩

[github-actions]

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