Set userVerification to preferred in registration options

[bradpurchase]

• In the authentication flow, userVerification is set to "preferred" so that user verification is only attempted when possible (i.e. biometric authentication methods like TouchID are presented when available, but it is not required for successful authentication).
• However, on the registration flow userVerification is not specified. Because of this, userVerification is required as this is the default in SimpleWebAuthn's verifyRegistrationResponse. This presents an issue during the registration flow when using iCloud Keychain or Chrome's built in passkey manager when no user verification method is available (e.g. when a MacBook is in clamshell mode and therefore TouchID is not present/available). In this case, the follow error is returned from authenticator.authenticate(): User verification required, but user could not be verified.
• This PR addresses this by specifying userVerification: "preferred" on the registration flow as well so that the user verification behaviour is consistent in both flows. This follows the guidance from web.dev on how to specify the userVerification parameter.

[alexanderson1993]

This is published.