In a kanban grouped by many2one with a progressbar, after emptying a column
by moving all records, the column wasn't correctly updated. This was causing,
in the best case, a record duplication or, in the worst case, a traceback.

This issue comes from the fact that, with a progressbar, a read_group is
performed each time a record is moved. When the group (column) becomes empty,
the read_group won't return this group even though the group still appears in
the kankan. When moving back the record in this empty column, there is a
desynchronization between the kanban controller data and the model.

To fix this issue, an option `keepEmptyGroups` is passed when performing the
mentioned read_group ; this mimics the kanban display that keeps empty groups
displayed and there is no desync anymore.

Fixes #23982