Fix UserGroup.Suggestion operation when a group is set with the groupRestriction parameter

The UserGroup.Suggestion operation does not handle all the use cases when the groupRestriction parameter is set, in particular the case where the user directory contains many entries and the search on this directory returns only a slice of users, where none belongs to the group set with the groupRestriction parameter.

Example:

1. The user directory contains 50 000 entries and is configured with a querySizeLimit set to 50.
2. The user suggestion widget is configured to return results when 0 character is typed and has the groupRestriction
3. None of the 50 first entries in the user directory corresponds to a user which belongs to the restricted group
4. A user clicks on the user suggestion widget
5. No entry is displayed

The expected behavior is to display the members of the group, and to limit the number of displayed items to the limit set on the user directory.

The implementation must be changed to filter the results from the group members first, and then to filter on the keyword filled by the end-user.