[Feature]: Grouping items
### What's the feature?

Hey team - love the work you guys do at tldraw. I was looking to group certain items and couldn't do it. This feature could be useful. Alternatively, if this does exist, can you point me to how to do it? 

### Where would you like this feature?

The tldraw.com website

### Contact Details

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct