More parse-dla fixes
this MR cleans up a bunch more isssues with the DLA parser:
- writes warnings to stderr consistently
- shows which file they error was found in
- create missing directories for missing years
- removes a trivial warning asking users to review the content since we are looking towards automating this process anyways
- deal with errata advisories separately
With this, I was able to import around 2400 missing repositories, with only 82 errors, partly due to reused DLA identifiers in the mailing list. Those will have to be handled by hand.
A separate merge request will add all those nice advisories in once bunch to catchup on a part of https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=859122