NUTCH-2931 Create OpenAPI specification for Nutch 1.x REST API

[lewismc]

This is a WIP I had on an old laptop and never pushed to my public Nutch mirror. My notes are that the OpenAPI spec didn't comply with the IBM/openapi-validator which is what I use(d) to lint and validate the OpenAPI specifications I work(ed) on over the years. I didn't have enough time/was side tracked by something or lots of other somethings and ultimately forgot about this branch altogether. I was surprised to find it.
I remember using the existing Java annotations and the Wiki documentation as resources for the OpenAPI. A few ex-colleagues also assisted in developing this branch.
It needs peer reviewed for completeness and updated to OpenAPI 3.1.X however this is a good foundation.
You can view the OpenAPI documentation if you copy and paste the content into https://editor.swagger.io/.
The goal would be to use the OpenAPI Generator project to generate a server implementation we could package either with Nutch or separately altogether.
I'm open to suggestions.

[lewismc]

I pushed a commit to add a new step to lint and validate openapi.yaml. I knew this would fail but it demonstrates where I got to last time around! Addressing the issues is non-trivial work.

  Total number of errors   : 89
  Total number of warnings : 315

In an API-first development model, these items would be addressed before we do anything further.