Customers - Customer entitlements

Problem Statement
As a developer, I am unable to read the entitlements on a customer record without chaining requests via the Core API to first fetch the customer object, then subscription, then reading the plan entitlements.
As an admin, I am unable to entitle a user for content after registration, as the entitlements are solely on a subscription.

User Story
As a developer, I would like to be able to set customer entitlements to grant them access to registration-only content, instead of subscription-only content.
Success/Acceptance Criteria
Create an entitlement-like field on the customer record that will allow an admin/developer to CRUD this value via Core and Open APIs.