For users of the Wikibase REST API to be aware of what functionality is available across the different iterations, we will implement an interface version of the API.

Acceptance criteria:

• Available at "/rest.php/wikibase/v[0]/openapi.json" is the OpenAPI document which incl. { "info" : { "version" : "0.1" } }

Notes:

• Once considered stable (1.0.0) the interface will be versioned following semantic versioning.
• This version of the schema document will be used to reflect non-breaking and breaking changes accordingly [TBD what this means]

Task breakdown:

• adjust our npm build:spec script to copy the openapi.json to the new location
• CI test that checks the built OpenAPI document against the source files
• create route handler that reads the built openapi.json file and returns it with the response