Add REST API version as a parameter

[kamil234]

As an enhancement, could we add a parameter to tabcmd so we can specify the server API version to use? Tableau server client library supports this, and it could be beneficial in:

1. Troubleshooting tabcmd issues to determine whether its a tabcmd issue or some sort of RestAPI version issue
2. Help avoid any regression in REST API by manually specifying server API version to manually fallback on a older version if needed

example usage:

tabcmd login -s -u -p --apiversion (optional) "x.x"