[Feature Request] The documentation is missing MessageBox.close method

### Existing Component
Yes

### Component Name
MessageBox

### Description
There's a MessageBox.close method in source code, which is used to close messages programmatically, however the docs page don't mention it, even when it lists imported MessageBox methods:
https://element.eleme.io/#/en-US/component/message-box#local-import

It'd be great to add info about that method, if it's intended to be used, or to provide an alternative to close messages programmatically, if using that method is discouraged

The simplest use case could be closing/canceling a message after a timeout