title: Terraform - How to restrict an input variable to a list of possible choices
body: <p>I have a variable that the user will input during run time. Lets say the variable name is region. However, I want the execution to be only successful if the user picks a value from one of the values defined in a list/ choices.</p>
  
  <p>how can I restrict it so the user's selection has to match values  that are considered acceptable in the variable definition?</p>