Allow layout Chart item series to be disabled

[DelazJ]

Feature description

1. In print layout, add a chart item
2. Add series
3. Assuming you are not happy with a series and don't want to show it (yet), your only option is to delete it. And recreate it later.

It should be possible to simply disable it, the same as we can do with a grid on a layout map item.

Additional context

And generally speaking, it could be nice if the series widget looked like the grid one, with option to reorder and copy