Returns True if the property has a concrete value set either via environment
        variables or on the froze profile instance.
        If a property only has a default value set, this returns False.

def has_prop_value(self, prop: typing.Union[str, EnvvarProfileProperty]) -> bool:
        """
        Returns True if the property has a concrete value set either via environment
        variables or on the froze profile instance.
        If a property only has a default value set, this returns False.
        """
        return self._loader.has_prop_value(self, prop)