Currently you cannot use these data attributes from within the container widget, but you can define class and style attributes.
It would be helpful for extensibility to be able as developer to define a data attribute and set a value.
Even better would be to make the value dynamically configurable.
I completely agree! We are trying to add Schema.org attributes to our page and still figuring out a way that works in our case.
If you are not using certain widgets like html snippet or rich text in your page then you can use the 'HTML Element' widget as a container.