JTAF API mode for binding to a webserver

[davedotdev]

This issue proposes an enhancement to JTAF, building on: #6, to introduce "REST API mode".

There is a plan to create a web UI for JTAF, in which a user instantiates JTAF with said web UI in a Docker container. For this container to issue work against JTAF, provide UI updates to the user and feel responsive, it's important that the UI can post information and retrieve updates and display them to the user, as well as provide download and upload facilities for input configuration and output binary download.

This proposal specifically focussed on a proposed REST API mode, invoked by starting the JTAF binary with an -api flag. In the config file a port should be presentable through a field for the API.

The API itself will provide utility for:

1. Uploading configuration, which will in essence be mapped to XML inputs into JTAF.
2. Selecting YANG models (the container when it's built will have them locally) through picking the platform and version
3. Select the CPU and OS architecture for the provider
4. Processing the provider
5. Receiving updates from the processing stages
6. Download the provider

A simple React web UI is proposed which connects to the JTAF REST API, not covered in this issue.

Let's discuss here.