Create a document reprocessing job

Creates a new job to reprocess an existing document without changing its file content. The job runs the processing settings saved on the document's collection, so changing those settings and reprocessing brings the document in line with what an upload to that collection would now produce, including dropping components those settings no longer call for. A document belonging to no collection, or to collections whose settings differ, is reprocessed with the full pipeline. Returns 400 for a 'pages' request against a collection whose settings have no single-page form (one reading the embedded text layer, which is read for every page at once, or one running no page stages); reprocess the whole document instead.