Please describe the use case(s) for this component

Now that mozilla/bedrock#11944 is complete, newsletter forms no longer rely on bedrocks' backend to post to Basket. There are still a few external sites that post via bedrock however, so we'd like to provide a go-to alternative here in Protocol that they can use / cherry-pick instead.

Please describe the change you wish to see

The JS code in bedrock should be moved into Protocol so that other sites can more easily use it.

Please describe why these changes need to be made

So that Mozilla sites can more easily post to basket without relying on bedrock.

Please provide any designs or prototypes of the proposed changes

N/A

Please describe where this component is currently in use

All Protocol newsletter component forms on bedrock currently use this code.

Please describe what this component should do in the following conditions

• When set in front of a dark background
• When set in front of a light background
• When viewed in a mobile/responsive viewport

N/A

Is the development of this component a blocking dependency for other work? Please explain if so

We'd like to remove the backend functionality from bedrock entirely, so making this happen would be helpful in providing an alternative.