Description of problem:
task query service method: getTasksByVariousFields does not make use of UserGroupCallback causing query not returning tasks that are assigned on group level.

Version-Release number of selected component (if applicable):


How reproducible:
Use HR example from jbpm-playground and then use REST api to start and get list of tasks with following url:
http://localhost:8080/kie-wb/rest/runtime/org.jbpm:HR:1.0/process/hiring/start
http://localhost:8080/kie-wb/rest/task/query?potentialOwner=katy

Steps to Reproduce:
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Actual results:
task list is empty

Expected results:
task list should contain task that are assigned to HR group where katy is member of that group

Additional info: