add REST documentation for mediacore module

Am I right in assuming this indicates that the full request body must be the serialized `MediacoreId` model object with `Content-Type: application/json` ?

If that's the case, I think a programmer reading the APIs can probably understand that it is the body of an HTTP request, and know how to use it, as opposed to needing a friend display name. A friendly display name will likely only become confusing for them if it makes them think it's some kind of parameter inside the body as opposed to just being the full request body.