SelectPanel2: Clean up stories (#3962)

* breaking changes + cleanup

* add SelectPanel.Warning

* add link styles

* remove todo story :)

* typo

* I not H

* change example from labels to assignees

* 1. make it work....

* move implementation details from story → component

* absorb EmptyMessage into SelectPanel.Message

* absorb WarningMessage into SelectPanel.Message

* absorb ErrorMessage into SelectPanel.Message

* stricter types for empty

* clean up lint errors

* tiny cleanup for bug

* clean up message types real good!

* child can be null

* types: first round

* types: round 2 - cleanup

* types: round 3 more cleanup

* types: 4 clean up stories ignores

* types: 5 clean up stories

* SelectPanel.Loading no longer exists

* Revert "SelectPanel.Loading no longer exists"

This reverts commit 0afa927.

* step 1

* default story - done

* split stories between examples and features

* remove default open from stories

* remove defaultOpen

* update playground

* default value for open

* tiny tweak!

* delete suspense key stories, we don't recommend it

* use TextInputProps for SelectPanel.SearchInput

* use loading on SearchInput for transition story

* add example for groups

* call storybook actions

Author: siddharthkp