Venmo - Support App Link Returns

[scannillo]

Epic: DTMOBILES-927 Jira: DTMOBILES-1163

Summary of changes

• Enable merchants to pass a appLinkReturnUri to VenmoClient
• Deprecate returnUrlScheme integration pattern

⚠️ Pending RCIP approval from Venmo side before merge & release.

Checklist

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

Authors

@scannillo