DataHeaderCnv will read the last DHForm in case of problems

This MR adds a functionality to find the last DataHeaderForm corresponding to the current DataHeader that is being converted P->T. DHForm is an extract of information common to many DataHeaders produced by the same Worker, but it can have several versions that grow incrementally as the info in DataHeader changes durting a job.
The last DHForm for a given worker should contain all information, so in case there is a problem reading the current DHForm, we can try to find the latest version and use it instead.
This is a better solution that I implemented recently in !60075 (merged) and it replaces it.