feat(passwordless): Fix issue of not being able to change auth factor selection

[mattcreaser]

• PR conforms to Pull Request guidelines.

Issue #, if available:

Description of changes:
If the user has already selected an auth factor then Amplify/Cognito doesn't allow you change the selection, but our passwordless UX does allow it. To support this we will keep track of whether the user has already selected an auth factor and, if they have, we will restart the flow with a preferred first factor instead.

So in summary:

• The first time a user selects an auth factor during signIn call confirmSignIn as normal.
• Any subsequent times an auth factor is selected call signIn with the selected factor as "preferred".

How did you test these changes?
(Please add a line here how the changes were tested)

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(liveness): message, fix(authenticator): message, fix(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[tylerjroach]

Not a big deal, but typo here.