Require password for superuser at plan phase

[winglot]

Add validation of password field for the superuser. Will now error on plan phase when superuser = true and password field was omitted.

#37

[mtesch-um]

Now the user can't import any superusers without managing their passwords with terraform :( I think that might be a common use case.

I guess personally if I had to choose between the two behaviors: 1. erroring only on apply vs. 2. not being able to import a superuser without having its password in tf state, I would choose evil 1. 😬

[mtesch-um]

This

resource "redshift_user" "user" {
  name      = "user"
  superuser = false
}

causes: │ "superuser": all of password,superuser must be specified