There is only one definition of Scrum: The Scrum Guide. The word "feature" appears only once and "chore" not at all.
The Product Backlog lists all features, functions, requirements, enhancements, and fixes that constitute the changes to be made to the product in future releases.
The idea that "anything that doesn't provide direct value to users should not be a feature" (or Product Backlog Item) is a Scrum mandate is a common misconception. It is a valid question to ask, "Should there be more focus on user value versus technical tasks?"
If the effort is purely a technical one and not providing new value, perhaps Scrum is not the best approach. Perhaps a Kanban model is more appropriate. Exposing services can be an opportunity for new integrations and sales (i.e. value) to existing or new users.
If Scrum is used, then it is up to the Scrum Team to determine how to best organize and manage the effort. It's a framework, put the processes and techniques in place that best support the needs of the team. Just keep it all within the roles, events, artifacts, and the rules or don't call it Scrum.
Scrum’s roles, artifacts, events, and rules are immutable and although implementing only parts of Scrum is possible, the result is not Scrum. Scrum exists only in its entirety and functions well as a container for other techniques, methodologies, and practices.