Add Buyer Phone Number Sent By Merchant to PayPalRequest

[agedd]

Summary of changes

• Adds a new field userPhoneNumber to the BTPayPalRequest so that the user can also pass in his/her phone number. as part of both one-time and vault flows.
• Add a new label and textfield in the demo app to allow for entering a phone number.
• Add sanity tests

Checklist

• [x] Added a changelog entry

Authors

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

• @agedd

[agedd]

marking pr as draft as API requirements are being finalized

[jaxdesmarais]

Closing PR as this work was pushed out

[agedd]

re-opening this pr as we need to add buyer phone number support