Allow creating only the types without any Client

[ibotty]

It would be great to allow generating only the types without any Client.

[ahl]

Interesting; can you explain the use case a bit?

[ibotty]

My use case is implementing a webhook for sftpgo where I need to return the user type (and its associated types).

Another use case I ran into (but I was not aware of progenitor then) was, if you want to reimplement an API. Of course the client will be useful for testing, but not neccessary (and might pull in too many dependencies).

I also assume that I won't run into some limitations of progenitor, because they seem only relevant when generating the client.