Read r2 draft in preview

Test that a modification made to an R2 article in Draft appears in the Preview API. Uses the R2 Newspaper Integration Endpoint. Runs on CODE by using the CODE config in application.conf.
CC @JustinPinner @guardian/contentapi @guardian/content-platforms 
I'd consider splitting this part up using whitespace and some comments to indicate the key logical steps here: e.g. something like:

    // build draft content
    ...
    // add to r2 using newspaper integration endpoint
    ...
    // verify that content is available in CAPI Preview environment
    ...