Change `vultr_user.acl` to typeset as the ordering is not important and causes extraneous plans

[F21]

Description

This PR changes the acl property in the vultr_user resource from TypeList to TypeSet. The order of the ACLs is not important and due causes a lot of extraneous plans when the order of the ACLs do not match the order returned from the server.

Related Issues

Closes #494

Checklist:

• [X] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [X] Have you linted your code locally prior to submission?
• [X] Have you successfully ran tests with your changes locally?

[F21]

Thanks for catching this! I updated the type assertions in the create and update functions.