enhanced email identity

Validations added to enhance email identity

Fixed error

Fixed error when to_emails=null

Fixed URL errors

Fixed URL errors

API Domain added

Added an option to create a sub-domain for API

Added API responses

Added/Updated proper integration responses for API endpoints

Added domain identify verification

Added code to verify domain identity

Module path fix

Fixed module path issue for finding lambda source code

Initial release

This Initial Release of terraform module will create a REST API to send Emails using Amazon Pinpoint