Demo App - Add text input for setting buyer email address

[tdchow]

Summary of changes

• Add text input for buyer email address in the PayPal flow

Checklist

• ~[ ] Added a changelog entry~
• ~[ ] Relevant test coverage~

Authors

List GitHub usernames for everyone who contributed to this pull request.

[scannillo]

A little late, but shouldn't this have gone onto main where MPE is live?

[tdchow]

A little late, but shouldn't this have gone onto main where MPE is live?

Hm, I believe it's planned to go out with the shopper insights feature which is this feature branch. Let's sync internally.