Change Campaign Experience event's Delivery ID, Campaign IDs data type to string

Right not it is integer value but it should be made generic by converting it to string.
## What are the schemas that are affected by the issue
Campaign/experienceevent.json

## What are examples of products that are impacted by the issue
ACS
Platform services

Open Campaign/experienceevent.json and locate the Delivery ID and Campaign IDs schema definitions. Confirm their current integer type and review nearby schema conventions before changing the affected fields to string; validate the schema and check the ACS and Platform services impact noted in the issue.

Written by the indexing model from the issue text.