[Bug] Role hierarchy level behaviour inconsist with document

[MuZhou233]

Describe the bug

In RBAC doc, we have following description:

Casbin's RBAC supports RBAC1's role hierarchy feature
...
For the built-in role manager in Casbin, you can specify the maximum hierarchy level.

But actually maxHierarchyLevel only affects HasLink.
Other functions like GetImplicitRolesForUser and GetImplicitUsersForRole ignore it and seeking infinity hierachy level.

To Reproduce

See description

Expected behavior

It would be better to have an consist behaviour.

[casbin-bot]

@tangyang9464 @JalinWang

[hsluoyz]

OK