Create process to rebuild the LatestIndex

[preaction]

There may be times where the latest index (ixlatest) table is out of sync with the CPAN uploads data (uploads). For those times, we should have a process we can run that will delete all the data in the latest index table and rebuild it from the CPAN uploads data.

Create a new process module, CPAN::Testers::Backend::RebuildUploadIndex. This should delete all the data from the LatestIndex resultset, and then rebuild it from the current uploads table.

This table is used to build reports, so it would be nice if downtime could be minimized.