feat: Add support for loading OAS contract from URL

[matteus6007]

Currently you only allow loading OAS contract from a file path, I require loading from a URL such as http://my-api.com/swagger/v1/swagger.json as the contract is dynamically created based on the models in the API.

[bethesque]

For the moment, your best bet is to use an HTTP client download the OAS to the machine where the publish command is running, and then publish it from the file path.