Move to public API ExecutableCommand

Fixed with https://github.com/kiegroup/droolsjbpm-knowledge/pull/314 https://github.com/kiegroup/drools/pull/1985 https://github.com/kiegroup/jbpm/pull/1281 https://github.com/kiegroup/droolsjbpm-integration/pull/1521 https://github.com/kiegroup/kie-docs/pull/940