Allows user interaction during the build process by prompting for input. To do so, it uses the configured InputHandler.
The prompt can be set via the message attribute or as character data nested into the element.
Optionally a set of valid input arguments can be defined via the validargs attribute. Input task will no accept value that don't match one of the predefined.
Optionally a property can be created from the value entered by the user. This property can then be used during the following build run. Input behaves according to property task which means that existing properties cannot be overriden.