Implement CITP Search Study Consent in the Core Add On

[jepstein]

Implements the consent component for the study (run npm run storybook and check the flow story by clicking on the "join study" button)

Text of consent can be found at https://docs.google.com/document/d/1yKTxV7aKMvgVaDe2Ug5h50byggqgptCtP6mA53CZzNw/edit?usp=sharing