Add changeset for #2986 (#3001)

### Background

Adds changeset for #2986, which was accidentally not included in that original PR.

### Solution

Adds the changeset.

### 🎩

N/A

### Checklist

- [x] I have 🎩'd these changes
- [x] I have updated relevant documentation

Author: MrGVSV

.changeset/afraid-yaks-pretend.md

@@ -0,0 +1,5 @@
+---
+'@shopify/ui-extensions': minor
+---
+
+Added `editable` Cart property