Expose types for the email events emitted by SES

## Describe the Feature

It would be nice if the SDK would provide types for the email events emitted by SES, [as documented here](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/event-publishing-retrieving-sns-contents.html#event-publishing-retrieving-sns-contents-mail-object).

## Is your Feature Request related to a problem?

Not necessarily a problem, but implementing it client-side is more error-prone due to misinterpreted documentation or possible future changes.

## Proposed Solution

Expose types for the email events body in the SDK.

## Describe alternatives you've considered

N/A

## Additional Context

I need these definitions in order to process email events.

## Your Environment
* AWS Java SDK version used: `2.16.81`
* JDK version used: `1.8.0_292`
* Operating System and version: `linux`