[POC] Generate node types command

This is just a quick sketch of a command to generate CND files (just namespaces and names, no properties / children definitions).

Obviously there is quite a large scope here, but just to follow on from <what was the issue where we discussed this?>
We can get a namespace URL from the bundle container extension, which is quite neat.

I also use the name of the extension as the alias, we could also use the bundle name (normally the difference between `acme_basic_cms` and `AcmeBasicCmsBundle`)