Add Mediasoup type interface for module itself

[piranna]

Feature Request

Add a type definition with the interface of what a Mediasoup-compatible object (an object with the same fields and static functions of the mediasoup export, if we consider the module exports as a singleton object), so we can easily identify what's a compatible one, at least at API level (for behaviour level we would need to also export the tests, like I have done in https://github.com/Mafalda-SFU/Mediasoup-node-tests).