Custom auth provider and custom auth domain got removed with an amplify auth update to change cognito triggers

**Is your feature request related to a problem? Please describe.**
So you want a custom domain for your auth resouce? Great
You also want to add another Auth Provider, like you own SSO portal running Keycloak? Great!

But then you also want to enable/disable/change some Cognito Lambda triggers. You run `amplify update auth` and suddenly everything is gone again. :( No longer is your custom domain added or your custom OpenID provider!

**Describe the solution you'd like**
The ability to not have everything get blow away when you want to update your Cognito Lambda triggers. Add a custom OpenID option for auth providers. Add a custom domain option for the auth resource.

**Describe alternatives you've considered**
- Manually adding everything back in!
- Running a script to update the `parameters.json` file used for setting up the Cognito Auth resource before running `amplify push`.

**Additional context**
https://github.com/aws-amplify/amplify-cli/issues/6701
https://github.com/aws-amplify/amplify-cli/issues/1880
https://github.com/aws-amplify/amplify-cli/pull/6499/files