New API docs - ReDoc version

[andy-a-o]

Currently we generate 2 versions of the API v3 docs from the OpenAPI spec, here they are:
https://losol.github.io/eventuras/openapi/v3/
https://losol.github.io/eventuras/openapi2/v3/

Both are not complete, and HTML is quite simple.

Probably it's better to generate the API docs using this:

https://github.com/seeebiii/redoc-cli-github-action