cross production tile archiving

[sbailey]

We need a mechanism for adding a daily/tiles/archive/TILEID/ARCHIVEDATE entry that references a separate data assembly production, e.g. archiving guadalupe tiles as superseding the previously archived daily production.

Currently desi_archive_tilenight archives within the daily production by moving daily/tiles/cumulative/TILEID/LASTNIGHT to daily/tiles/archive/TILEID/ARCHIVEDATE and creating a link from the original cumulative directory to the archived directory. This new form of archiving would be the reverse: the link would be daily/tiles/archive/TILEID/ARCHIVEDATE pointing to the appropriate directory in guadalupe/tiles/cumulative/TILEID/LASTNIGHT (which will be write protected and frozen, i.e. archive-eligible).

With that link, and a matching update to surveyops/ops/tiles-specstatus.ecsv ARCHIVEDATE column, the new reference production will get picked up by MTL updates.