Add a query parameter to JSON response for minimal data

Problem/Motivation

JSON response is ~2.7kB (likely differs depending on metadata from the song).

I should add a query parameter to the feed that reduces the data to only what is needed for the custom Block to display. This should significantly reduce the amount of data being pulled via AJAX.

Steps to reproduce

Observe network requests to endpoint in developer console.

Proposed resolution

Add a parameter `reduced` to the JSON endpoint which will only return items necessary for the custom Block to display, omitting all other data.