Original User Agent

## What are the schemas that are affected by the issue
xdm/context/browserdetails.schema.json

## What are examples of products that are impacted by the issue
Adobe Primetime Authentication.

## Description
Sometimes the UserAgent details provided by third party data collection systems alter the UserAgent string. PrimeTime would like to propose that we add a `xdm:originalUserAgent` to the xdm/context/browserdetails.schema.json

Start with xdm/context/browserdetails.schema.json and review the existing property definitions and naming conventions. Add the proposed xdm:originalUserAgent field in the appropriate schema section; the work is done when the schema represents the original User Agent value consistently with its surrounding fields.

Written by the indexing model from the issue text.