Implement FL Authentication and Cycle API Request

[mjjimenez]

This will be implemented in SyftClient class start method here : https://github.com/OpenMined/SwiftSyft/blob/master/SwiftSyft/Classes/SyftClient.swift#L28

The API requests are described here:
OpenMined/PyGrid-deprecated---see-PySyft-#445
Refer to Authentication with PyGrid and FL Worker Cycle Request

The requests can be made by socket messages or HTTP requests but this issue is mainly for the HTTP requests made using URLSession.dataTaskPublisher and chaining the requests.

A seperate issue will be made for using signalling requests.

[ghost]

@mjjimenez Please, assign it for me

[mjjimenez]

@SashaBataieva for the PyGrid API here, they're not live yet but we can proceed with creating the requests on the iOS side for now.

You can follow the updates on that issue here OpenMined/PyGrid-deprecated---see-PySyft-#445

If you have any questions regarding Combine framework, and URLSessionDataTask publisher, we can discuss it here or in slack. I'm just starting to familiarize myself in using it too.

[mjjimenez]

Closed by #60