[task] Add openapi generator that will generate an osgi ready client for OpenAPI specification build by API Platform

- use https://github.com/OpenAPITools/openapi-generator, https://openapi-generator.tech/docs/generators/java as a starting point and customize templates

Start with the OpenAPITools generator and the Java generator documentation linked in the issue, then determine how their templates can be customized for API Platform output. The work is done when the generator produces an OSGi-ready Java client from an API Platform OpenAPI specification; the issue does not name repository files or tests to run.

Written by the indexing model from the issue text.