Clean up and document REST API

The current REST API was designed and implemented organically, so it is not always internally consistent, which in turn hinders the ability to use common code to generate and consume responses. There are also places where it doesn't follow best REST practices.

This top level ticket collects the various things that we need to do as part of this.

Acceptance criteria

• Revised protocol which follows best practices
• Swagger/OpenAPI definition which matches the implementation
• both web client and server updated to new protocol

Alternatives considered

Leave things as they are

Additional context

This cleanup is independent of any decision as to whether to support the API for external use by anything other than the OpenRefine web client. That would require a protocol test suite, additional documentation, and perhaps supported client libraries.

No files, tests, or entry points are named. Begin by mapping the current REST protocol across the web client and server, then define the revised protocol and corresponding Swagger/OpenAPI definition; done means both implementations match the revised protocol.