Add the EE region information to the Web SDK mixin

## What are the schemas that are affected by the issue

- aep-web-sdk-experienceevent.schema.json

## What are examples of products that are impacted by the issue

Experience Edge

Start with aep-web-sdk-experienceevent.schema.json and locate the Web SDK mixin that represents Experience Edge data. Confirm the existing schema structure and determine how EE region information should be represented; done means the schema includes that information and remains valid.

Written by the indexing model from the issue text.