DEV: Refactor the api docs for the user endpoint (PR #14377)

Due to the way that rswag expands shared components we were getting this warning when linting our api docs:

Component: "user_response" is never used.

This change refactors the api/users_spec.rb file so that it uses the new way of doing things with a separate user_get_response.json schema file rather then the old way of loading a shared response inside of the swagger_helper.rb file.