You can model your code after RepositoryEntriesWebService but without the @OpenAPIDefinition annotation. There must be only one unique @OpenAPIDefinition annotation in the code for the documentation.
Your web service will be discovered by the Spring framework. You have several XML configurations like restApiContext.xml with the line:
<context:component-scan base-package="org.olat.restapi,org.olat.restapi.security,org.olat.restapi.system" />
The package where your HypRepositoryEntriesResourceWebService stay need to be in one of the packages declared in these <context:component-scan>. For performance reasons, we don't have auto-discovery.
If you want that your HypRepositoryEntriesResourceWebService appears in the documentation, you need to add the package in the bean declaration:
<bean id="openApiFeature" class="org.apache.cxf.jaxrs.openapi.OpenApiFeature">
defined in restApiContext.xml (there is a list of packages here too).
Best regards
Stéphane