Documenting airgapped deployment modes

[fabriziofiorucci]

NGINX airgapped use cases are fairly common at least across EMEA. It would be great/useful to enhance the docs adding sections with howtos for (in order of priority):

• Unprivileged/non-root NGINX deployment on k8s & openshift
• Airgapped NGINX Plus installation on VM not using MyF5 (prospects have no access to it - this helps presales)
• Airgapped NIM installation on k8s & openshift using Helm
• Airgapped NAP

[JTorreG]

This will need to be broken down into separate tasks for each product