[terra-functional-testing] Update Upgrade Guide

[benbcai]

Story

Description

As a maintainer of terra-functional-testing, I would like the update the the documentation and upgrade guide

Motivation

So that any additional helpful information can be included to help teams have a smooth transition when upgrading.

Definition of Done

We'll know we're done when the documentation and/or upgrade guide include the following information:

• formFactor and locale are no longer accessible from the browsers.options object. They are no accessible from the Terra.serviceOptions object.
• The browser object is no longer accessible outside of the it block. It can only be accessible inside the it block due to how the ordering of the lifecycles hooks are changed. See before hook executed after describe block in test webdriverio/webdriverio#6119.