[Bug] the subpages should be automatically deleted when the root page is removed

### Bug Description

The subpages should be automatically deleted when the root page is removed.

### How to Reproduce

1. Create page 1.
2. Create page 2 within page 1.
3. Permanently delete page 1.
4. Search Page 2.

### Expected Behavior

Page B should not appear in the result.

### Operating System

Desktop

### AppFlowy Version(s)

0.6.4

### Screenshots

_No response_

### Additional Context

_No response_