Docs for Ambassador 2 + fixes for preview breakages (#174)

* Add docs for ambassador 2.0 generator usage

* make host option mandatory. Introduce template func for splitting a comma separated string into its components for the mapping template cors section as Ambassador 2.0 doesn't support comma separated strings as paramters for cors anymore.

* host option is now mandatory for Ambassador 2.0 as AmbassadorMappings must match an AmbassadorHost resource in order to work

* host option is now mandatory for Ambassador 2.0 as AmbassadorMappings must match an AmbassadorHost resource in order to work

* split CORS comma separated strings into array using template func and iterate over them creating a yaml array in the resulting AmbassadorMapping resource

* Add warnings to Ambassador 2.0 docs regarding unstability of the Developer Preview

README.md

@@ -50,11 +50,13 @@ allowing you to
 
 Kusk currently supports (click for configuration options)
 - [Ambassador 1.x](https://kubeshop.github.io/kusk/ambassador/)
+- [Ambassador 2.0](https://kubeshop.github.io/kusk/ambassador/)
+  - **Warning** This is a developer preview and should be treated as unstable
 - [Linkerd](https://kubeshop.github.io/kusk/linkerd/)
 - [Nginx-Ingress](https://kubeshop.github.io/kusk/nginx-ingress/)
 - [Traefik V2 (v2.x)](https://kubeshop.github.io/kusk/traefik/)
 
-Some of the upcoming tools we'd like to support are Kong, Ambassador 2.x, etc. Please don't hesitate to 
+Some of the upcoming tools we'd like to support are Kong and Contour. Please don't hesitate to 
 suggest others or contribute your own generator!
 
 ## Documentation & Support