feat(app-probe-proxy): add document for application probe proxy

[jijiechen]

fixes https://github.com/kumahq/kuma-website/issues/1887

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[jijiechen]

Preview location:

• Application probe proxy: https://deploy-preview-1888--kuma.netlify.app/docs/dev/policies/service-health-probes/#application-probe-proxy
• Pod annotation: https://deploy-preview-1888--kuma.netlify.app/docs/dev/reference/kubernetes-annotations/#kumaioapplication-probe-proxy-port