Allowing to generate a components file only

[asafh]

Is your feature request related to a problem? Please describe.
I would like to have a gradual migration to Spot. I would like to start describe components using Spot and then reference them from my existing OpenAPI definition file.

Describe the solution you'd like
I would like to have the required @Api specification removed and also have spot generate components definitions for interfaces exported (or a different way to mark these - as we can't decorate interfaces)

Describe alternatives you've considered
An alternative is to use a dummy @api with a dummy @endpoint and just ignore these sections in the output