Added sign-in-sign-up-passwordless custom policy

[rbrayb]

This allows sign in and sign up passwordless custom policies.

As B2C requires a password to create a user, a random password is created by the custom policy.

[JasSuri]

Is this different from samples/policies/passwordless-email?

[rbrayb]

Yes, I believe so.

The key here is that the sign-up automatically creates a random password.

The sign-up screen does not ask the user to enter a password since that makes no sense in a passwordless flow.

The user is not aware that a password has been created for them.

I couldn't find any examples of a signup flow doing this hence the submission.