Provide Engage functionality on requested digitisations

At present, the only way to enable Engage on a digitisation of a book or journal scan is for the academic creating the list to upload the scan themselves. For institutions like ours, where all scanning is done centrally by the Library via the "Request digitisation" process (for reasons of copyright compliance, accessibility and workflow), this means Engage is of extremely limited use - so much so that we have abandoned our intended pilot of it. Please make the Engage functionality available on scans added via TADC using the "Request digitisation" option.