Update Journey Version Step Events XDM Mixin to add attributes related to CJM reactions

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

https://github.com/adobe/xdm/blob/master/extensions/adobe/experience/journeyOrchestration/stepEvents/journeyStepEventCommonFieldsMixin.schema.json

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

Journey Orchestration, Customer Journey Management

Start by reading extensions/adobe/experience/journeyOrchestration/stepEvents/journeyStepEventCommonFieldsMixin.schema.json and inspect related Journey Orchestration and Customer Journey Management schemas. The issue does not identify the CJM reaction attributes or their expected definitions, so clarify those requirements before changing the mixin; done means the agreed attributes are represented in the affected schema.

Written by the indexing model from the issue text.