Unable to have devices remembered and force MFA sign in every time

[trahim]

We are having issues having our devices remembered in our device configuration but not forcing MFA to be required on every sign in. This because both device_configuration_device_only_remembered_on_user_prompt and device_configuration_challenge_required_on_new_device cannot be false if they are it defaults to an empty list and no device configuration is set. This is on line https://github.com/lgallard/terraform-aws-cognito-user-pool/blob/master/main.tf#L257
Picture attached of what I would like to have set in the UI.

I've made a PR that has fixed it for our use case I'm not sure if this will have repercussions on other cases I haven't checked but I don't think so.

#123

[xronz]

@trahim I did a hotfix, and you can refer to the following issue

#124