[JAVA] [jaxrs-spec] add custom method to add/remove elements from Java Collections

Created by: wolfdale

Description

Generate methods to add & remove elements from Java Collections

openapi-generator version

v4.3.1

Command line used for generation

/bin/jaxrs-spec-petstore-server.sh

Steps to reproduce

1. Execute - ./bin/jaxrs-spec-petstore-server.sh
2. Generated code doesn't include methods to remove or add elements to Java Collections.

Related issues/PRs

Suggest a fix/enhancement

Make changes to JavaJaxRS/spec pojo.mustache to generate add/remove methods.