* Add AsyncVirtualizedSelect component in grafana-ui
* Slice FolderPicker results to 1k and virtualize list using AsyncVirtualizedSelect
* Group list in alert form: Use AsyncSelect and slice results to 1000
* Virtualize and slice always in FolderPicker: set default sliceResults value and let consumers change this value
* Always slice results in FolderPicker
* Limit folder results setting the limit in the api call instead slicing in the FE
* Remove warning about the limit in the Select label