Determine goals and non-goals for Gateway API Dev Preview

Document goals and non-goals for dev preview release of Gateway API of Istio.

Goals

• User will be able to install Istio with Gateway API enabled for Ingress without requiring Service  Mesh to be enabled.
• We will document how to use istioctl to install Istio, using a blog post or OKD documentation. 
• Users will be able to use GatewayClass, Gateway, and HTTPRoute to expose a real-world (non-production) application to the Internet.

Stretch goals

• We will document how to use External DNS Operator to configure a wildcard DNS record for Gateways. 
• An operator will automatically configure a load balancer and DNS for gateways. 
• If OSSM is ready for use as an installer in Dev Preview (no bugs, issues with release cadence worked out, etc) we will document how to use OSSM to install Istio.

Non-goals for Dev Preview

• We will not (necessarily) provide an operator to manage Istio once installed. 
• We will not support reencrypt termination.
• We will not document anything in OCP product documentation. 
• We will not implement CI for Istio. 
• Users will not be able to use TLSRoute, UDPRoute, TCPRoute, policy attachment, or other features that are still alpha in Gateway API or that Istio does not currently support. 

Open questions

• Will we be using images built by the Service Mesh team, images we build, or upstream images?