DEVDOCS-6580 - Prevent order migration when a new Company user is added from the storefront

[bc-Vince]

DEVDOCS-6580

What changed?

• The Create a Company User S2S endpoint information now indicates what happens to existing orders from previous B2C customers converted to B2B Company users.

Release notes draft

• Included a callout to the REST Management Create a Company User endpoint that a user's existing orders are migrated to the Company's Buyer Portal.
• Included information on how to migrate a user's existing orders after creating their account with the REST Storefront API or the GraphQL Storefront API.

Anything else?

ping @bc-terra