Apple SSO: Create Flow

[chipsnyder]

📘 Project: #381	Depends on: https://github.com/Automattic/pocket-casts-ios/pull/394

Adds the upsell flow to the account creation process.

📓 In my testing, Apple SSO didn't always return the email in the simulator, so testing with a physical device is recommended.

To test

1. Enable the Feature Flag signInWithApple
2. Set your scheme to Staging
3. Login with SSO using an account that isn't in Staging (you can also use hide my email to create a new account)
   • TODO: The endpoint doesn't handle new accounts yet.
4. Expect to see the upsell flow.
5. Complete the flow for a Free Account and again for a Paid.
   • TODO: I wasn't sure yet how to handle payment methods in Staging using IAP.

Checklist

• [ ] I have considered if this change warrants user-facing release notes and have added them to CHANGELOG.md if necessary.
• [ ] I have considered adding unit tests for my changes.
• [x] I have updated (or requested that someone edit) the spreadsheet to reflect any new or changed analytics.

[CLAassistant]

All committers have signed the CLA.