Add `userAuthenticationEmail` to 1-Time Checkout

[scannillo]

Background

• See Android PR https://github.com/braintree/braintree_android/pull/978/files

Summary of changes

• Add userAuthenticationEmail property to BTPayPalCheckoutRequest
• Expose text field for email in Demo
  • Cherry-picked demo app UI updates from this App Switch PR (https://github.com/braintree/braintree_ios/pull/1273)

Demo UI

Checklist

• [X] Added a changelog entry

Authors

@scannillo

[scannillo]

Update the base branch to be for the ShopperInsights feature based on convos that E2E testers will be testing this alongside ShopperInsights and the 2 features are "planned" to be released together.

[sarahkoop]

Are we seeing the same success in sand and error in prod as we are on Android?

[scannillo]

Are we seeing the same success in sand and error in prod as we are on Android?

I'm seeing this work in sandbox, but am not seeing the email prefill in production. I don't see a specific error in production though. @tdchow - what error in prod are you seeing?

[sarahkoop]

Are we seeing the same success in sand and error in prod as we are on Android?

I'm seeing this work in sandbox, but am not seeing the email prefill in production. I don't see a specific error in production though. @tdchow - what error in prod are you seeing?

Confirmed it's expected to not be passed in prod currently (prod has not been released) - should not block merging this PR, we will hold on the full feature merge/release until this is rolled out in prod

[tdchow]

I'm seeing this work in sandbox, but am not seeing the email prefill in production. I don't see a specific error in production though. @tdchow - what error in prod are you seeing?

Apologies! I wasn't seeing a specific error, but I was not seeing email prefilled in the live environment, same as iOS.