Add site properties to site model and site functions #776

I recently had to write a script to create and configure several new sites on tableau server. There are several options for the create and update site api endpoints that are not in the site_model or the site functions.

I was able to work around this by just scripting http requests to the endpoint. This solution is not a good one though as it will require maintenance to the script on my end whenever switching versions or updating servers. This also leaves my code for managing tableau fragmented because for most of it I use the tableau server client but now I have the supporting scripts. I would like to do everything with the tableau server client for the sake of maintainability.