"As a Curator, I want to get a server-rendered HTML representation of the difference between two revisions, so that the difference of non-main slots is presented in the preferred way."

This is a modification to the endpoint defined in T231347: Curator compares revisions, to add HTML output as well as JSON output.

The URL accepts a format parameter, which can be json or html; with json the default.

The output is:

Body: JSON, an object with the following fields:

• from: object containing {id: first ID, identical to id parameter}
• to: object containing {id: second ID, identical to other parameter}
• diff: an HTML fragment representing the differences of all slots, main and non-main slots