Add possibility of defining a "prefix" for the API path

[maticardenas]

When defining an OpenAPI specification, the correct and expected way is to not include any path within the servers URLs (https://example.com).

However, it could be the case that old APIs have already defined a server URL that way (https://example.com/api/v1/pets/tasks/), or maybe the fact that a very long common same path exists makes it easier to define it in the server URL, leaving to shorter and clearer paths in the endpoints themselves.

Given that the package currently ignores the server URL, the fact of not retrieving the necessary prefix from this server URL will make the tests to fail given the path won't be found.
A prefix functionality could be introduced, in order to handle these scenarios.