`amplify update auth` command should show the existing settings

**Is your feature request related to a problem? Please describe.**

If I run `amplify update auth` it provides a complicated series of questions to answer. It’s hard to remember what values were chosen the first time around.

**Describe the solution you'd like**

It would be really helpful if it showed me the existing value for each one during each step.

**Describe alternatives you've considered**

Trying to read through my cloudformation files?

**Additional context**

This came up because I wanted to update my project to include hosted UI info as specified here: https://github.com/aws-amplify/amplify-cli/issues/844#issuecomment-479583969