[feature] How to get group tree with casdoor-nodejs-sdk?

[radiorz]

The group tree means this part: https://door.casdoor.com/trees/built-in

The group tree mainly relies on the data returned by the get-groups API. But the returned data is a list. The Casdoor frontend code will build the tree from the list. We may need to do so too. There are two ways:

1. Build the tree in Casdoor Go backend: https://github.com/casdoor/casdoor/blob/master/controllers/group.go#L31
2. Build the tree in the SDK (like this casdoor-java-sdk)

[casbin-bot]

@tangyang9464 @JalinWang @imp2002

[hsluoyz]

Fixed by: 02c17eb

[hsluoyz]

@radiorz use the new API: getGroups(withTree?: boolean)