Add optional DOTENV_IT token pulls to fail on pull if containing a blank value

[motdotla]

An easy mistake for both developers and devops to make is to forget to set a value for an environment variable before deploying. Add an optional flag that raises an error if this is the case - when pulling. This will cause a stacktrace and prevent the deployment from going out. Then the development or devops team can set the value and redeploy.