doc: Full documentation as per v0.11 (l7mp#40)

Rewrite intro, user guides and manuals, plus create a separate standalone deployment doc: 
* [Why STUNner](/doc/WHY.md)
* [Deployment models](/doc/DEPLOYMENT.md)
* [Concepts](/doc/CONCEPTS.md)
* [Getting started](/doc/INSTALL.md)
* [Gateway API reference](/doc/GATEWAY.md)
* [Security](/doc/SECURITY.md)
* [Authentication](/doc/AUTH.md)
* [Standalone mode](/doc/OBSOLETE.md)

Generate new Helm version to match the docs

Test: Update helm CI

Fix Dockerfile missing internal packages

Implement WithOptions to pass options to NewStunner

Upgrade CI

Remove vnet.Net from the public STUNner API (we use vnets for testing)

Add PublicAddr for STUNner listener config

This field will be filled in by the operator by finding the service associated with the
listener (containing the listener's name in the annotation
"stunner.l7mp.io/related-gateway-name"). We do not use this field right away, but it will be
useful later for generating ICE server configurations in the WebRTC application server.

Make sure stunnerd picks up the loglevel from the config file

Milestones update