Pass down extra props to group header as item.data (#3046)
Pass down extra props to group header as item.data (#3046)

* pass down extra props to group header as groupHeaderProps

* allow items-specific headingProps

* Prettier change

Co-authored-by: Thomas Walker <b1248da4ea4d8cc0f52611605b697ab5d6eed614@me.com>
Co-authored-by: Nathan Bierema <a6fca4d50c35000ae1d7c4c67bfdcdf64e0204e4@gmail.com>
Co-authored-by: Jed Watson <ed0ad9995ea3c245e179483e2832a783933b78c0@me.com>
JedWatson/react-select,JedWatson/react-select