Need Auxiliary Properties to be part of Experience Event Schema

Audience Manager accepts auxiliary properties from other solutions and third party providers which are basically key value pairs and do not have fixed set of keys (within a provider or across providers). These properties can be best captured as a map with in an instance of XDM. This will help in providing more context and information to the current instance of XDM.
This need not be limited to Audience Manager requirement but generic requirement as a whole.

## What are the schemas that are affected by the issue
Experience Event (Others later)

## What are examples of products that are impacted by the issue
Adobe Audience Manager
Adobe Cloud Platform

Start by locating the Experience Event schema and reviewing how it currently represents properties and maps. Define how arbitrary provider-supplied key-value pairs should be represented without fixed keys, then confirm the schema accepts the proposed auxiliary properties and document the affected Experience Event behavior.

Written by the indexing model from the issue text.