storybook: Fix Backspace in Auto Height Editor and Picker stories (#11011)

Currently in the *Auto Height Editor* story the backspace key is not
working when you type into the Editor.

The same thing is true for the *Picker* story as one is not able to
backspace...

By adding an entry in the keymap file

```rust
assets/keymaps/storybook.json
```

both of these issues are solved...

Release Notes:

- N/A