Allow quick pick items to always be visible and sticky

Based on internal discussions, would like to have an option in the Quick Pick item API to allow certain items to be grouped together and separated by a border. Additionally, when there are long entries in the list, it would be great to have this group always visible like below (see items at the bottom of the quick pick): <img width="648" alt="CleanShot 2021-08-18 at 13 53 40@2x" src="https://user-images.githubusercontent.com/35271042/129970755-5b43f2ea-2f2c-4076-a6ef-5df7f3cd0afd.png"> And when filtering the list, it would filter as it normally does: <img width="633" alt="CleanShot 2021-08-18 at 13 56 13@2x" src="https://user-images.githubusercontent.com/35271042/129971045-3907bf17-db01-458c-a1b1-999c3e76f2a7.png"> <img width="627" alt="CleanShot 2021-08-18 at 13 56 20@2x" src="https://user-images.githubusercontent.com/35271042/129971057-c2318503-8641-468c-98c1-8ba39928faf2.png"> cc @luabud