Adyen Dropin Checkout

[bbengfort]

Scope of changes

Adds an Adyen dropin session for checking out. This is done in the simplest way possible for demo purposes and will need to be refactored to better JS and front-end techniques.

Type of change

• bug fix
• new feature
• documentation
• other (describe)

Acceptance criteria

This will be merged without review.

Author checklist

• I have manually tested the change and/or added automation in the form of unit tests or integration tests
• I have updated the dependencies list
• I have added new test fixtures as needed to support added tests
• I have added or updated the documentation
• Check this box if a reviewer can merge this pull request after approval (leave it unchecked if you want to do it yourself)