Implementation of internal drag & drop missing two pieces

[bertbarabas]

Currently you can set:
row_drag=True,
in a columnDef

but to turn on the managed version of drag & drop must use custom_attrs:

custom_attrs={"rowDragManaged": True},
in the ag_grid

but then there is no support for:
on_row_drag_end=SomeState.on_row_drag_end

To complete the the implementation for internal drag & drop we need:

1. add row_drag_managed prop to ag_grid
2. add the event on_row_drag_end to ag_grid

[linear]

ENG-4465 Implementation of internal drag & drop missing two pieces