Add support for starting the latest "version" of process using process name in the kie server REST endpoint

We already have the ability to call a subprocess by name and start with the latest "version" of the process definition. This is done using the same process name, different id, and different version. The called element is manually inputted as the process name.

https://github.com/kiegroup/jbpm/blob/master/jbpm-flow/src/main/java/org/jbpm/workflow/instance/node/SubProcessNodeInstance.java#L175

But we don't expose that in the REST API. Currently the only way to start a process is through the /server/containers/

/processes/

/instances call. But using the process name for the processId doesn't work here.