Add list router sdk

[deadlycoconuts]

Context:
Currently the Turing SDK only supports batch experiments by covering only operations related to ensemblers and ensembling jobs, and we are now expanding its scope to cover online experiments by extending the SDK to cover operations involving other Turing components.

Changes:
This PR involves implementing a functionality corresponding to one of the API endpoints involving routers, i.e. listing the routers belonging to a given project.

• A new SDK class Router has been created for users to interact with (this interface exposes some attributes such as id, name, project_id, config, etc.)
• The schema in the OpenAPI spec for ExperimentConfig has been changed to remove usage of the oneOf keyword, which isn't currently supported by the OpenAPI generator
• The schemas in the OpenAPI spec for certain components in Router and its constituent components have been modified slightly to allow for null responses and other minor schema differences
• A new test script for the new Router class' list method with its corresponding test fixtures (which can be reused when extending the SDK to other components)

Note that the massive number of new line additions stem from the autogenerated OpenAPI classes.

[romanwozniak]

All good now 🚀