API for Swagger (service definitions) import

We have 3scale-cli https://github.com/3scale/3scale-cli/blob/master/docs/import-api-definition.md that does a swagger import to API Manager and creates the services definition. This is a great feature since all customers now rely on swagger as the source of truth.

Expose this as an API

This is part 1 for THREESCALE-2809

Dev notes

We can port the logics that parses the OAS spec and creates the multiple objects in system from the toolbox into system, make it an API endpoint in system and then the toolbox could be updated to use that endpoint instead.