DTP/DUP: add new IDs to replace internal Django ids in the UI

Same change to be done as was done for studies and DOs.
New IDs will start with DSRT-{number} for DTPs and DSRU-{number} for DUPs.
This will close #7 and #20.

Start by tracing how study and DO IDs were added to the UI, then locate the corresponding DTP and DUP display and data paths. Confirm the existing identifier format and identify the tests or UI checks covering those views. Done means DTPs show DSRT-{number} and DUPs show DSRU-{number} instead of internal Django IDs, with the related cases for #7 and #20 covered.

Written by the indexing model from the issue text.