REST operation to query all attributes of a user
Unity allows for getting attributes of a user in a specific group over the REST API. This task is to introduce another capability: get attributes in all groups the user is member of.
Additional feature: allow for limiting groups with ant-style path patterns (as URL query param)
This functionality should be exposed under a new path and returned JSON should be grouped by group, i.e.: [group1->[attributesIngroup1], group2->[attribtuesInGroup2], ...]
Note - dev-3.4 branch.