Add API endpoint for retrieving autocomplete options

Problem/Motivation

It would be useful to have access to a list of autocomplete options to be able to implement autocomplete searches on the client, rather than having to make request to Drupal on the client side. This is something we are already utilizing in the Next.js Webform library.

Proposed resolution

Add API endpoint for retrieving autocomplete options

Remaining tasks

User interface changes

API changes

Data model changes