[Bug] Hard to scroll horizontally to see more groups in Kanban

### Bug Description

When there are a lot of groups on the Kanban board, it's hard to scroll horizontally to see more because there is no horizontal scrollbar at the bottom of the window

### How to Reproduce

Create many groups until the number of groups exceeds the visible area of the screen

### Expected Behavior

Add a horizontal scroll bar

### Operating System

macOS

### AppFlowy Version(s)

0.13.2

### Screenshots

### Additional Context

_No response_