feat(core): add AmplifyOutputs types based on the CLI Gen2 client config schema

[NikaHsn]

Issue #, if available:

Description of changes:

• add AmplifyOutputs types representing the CLI Gen2 client config schema
• updated CognitoUserAttributeKeyConverter to not convert keys to upper case and add a new CognitoUserAttributeKeyConverterToUpperCase for converting keys to upper case (this is only used by AmplifConfig as the user attribute keys are upper case in the amplifyconfiguration file)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.