feat(authenticator): Support passwordless signUp

[mattcreaser]

• PR conforms to Pull Request guidelines.

Issue #, if available:

Description of changes:

• Adds ability for user to sign up without a password.
• Adds ability for password and confirmPassword fields to be optional in signUpForm. This allows for signups with optional passwords.
• If password field is specified in signupForm but confirmPassword is not specified, we will no longer automatically add the confirm password field (fixes the confirm password field should not be mandatory in SignUp #166)

How did you test these changes?

• Verified passwordless sign up flow completes successfully.

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.