Add Swagger UI for our REST APIs

[emersion]

Who would benefit from this feature?

Developers

What is this feature about?

It would be neat to add a Swagger UI to the osrd.fr website with our REST APIs.

The Swagger UI looks like the right hand side of this page: https://editor.swagger.io/

Why is this feature valuable?

Would make it easier to explore the API schema and understand the data formats it accepts/returns.

Anything else people should know?

No response