Investigate how to build REST API generated docs

[dmuelle]

As well as the Liberty API/SPI docs, there are some OpenAPI REST API docs in IBM Docs that Alasdair has previously said do need to come over the OL docs. These are API docs generated by OpenAPI for APIs that are provided to use with Liberty (Batch REST APIs, and JMX REST Connector REST APIs) (so, to be clear, this has nothing to do with the OL support for MicroProfile OpenAPI etc).

Note that the current API REST API documentation in IBM Docs is incomplete- missing the config and validation endpoints for example.

Discussed in 10/5 website meeting- lower priority than pending infrastructure and translation issues.

Corresponding issue in docs repo: OpenLiberty/docs#3428