Add support for expanding reference fields

[XtraSonic]

Previously requests which included the "fields" query parameter were made with .../api/shared_spaces/<space_id>/workspaces/<workspace_id>/defects?fields=author,release,phase,priority,team. Octane used to return more information about reference fields, but this functionality was changed. Now it only returns enough information to identify the reference field without additional information. Octane also added a way to query extra fields for reference fields using the following format .../api/shared_spaces/<space_id>/workspaces/<workspace_id>/defects?fields=author{name},release,phase{name},priority,team and we also need to support this feature in the sdk

[radislavB]

What methods in EntityService you need to use?