Deprecate and remove mod_security feature

[rikatz]

mod_security feature today presents a challenge for ingress-nginx.

Its compilation takes a very long time, its support is gone from the community, the usage is not straightforward and there is no replacement for it.

This way, the understanding is that people should at this point rely on a WAF solution in front of ingress-nginx or on the endpoint, while this can be re-analyzed and re-implemented as a different solution in the future

/kind deprecation

[k8s-ci-robot]

This issue is currently awaiting triage.

If Ingress contributors determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

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[github-actions]

This is stale, but we won't close it automatically, just bare in mind the maintainers may be busy with other tasks and will reach your issue ASAP. If you have any question or request to prioritize this, please reach #ingress-nginx-dev on Kubernetes Slack.