Entity Picker property editor

[bjarnef]

Currently many property editors allow to configure these as single/multi pickers like Media Picker, Multi URL Picker, MTNP etc. although it is not handled consistent.

However some property editors doesn't allow this, e.g. Member Picker is only a single picker and Member Group Picker is only a multi picker.

I suggested this some time ago to configure Member Picker as multi picker, but it may introduce breaking changes unless it is introduced as a new property editor.
#7634

Maybe something like an entity picker similar to the one @mattbrailsford added to Konstrukt could be useful. https://docs.getkonstrukt.net/property-editors/entity-picker#configuring-an-entity-picker

We already have MNTP, which works for Content, Media and Member. But it probably doesn't make sense to add Member Group to this as well.