Reduce size of the cache file by keeping only packages available in Apertis

Currently, the cache file is quite big ~ 70MB and parsing it during the packaging-data-fetch-downstream job gives frequent out-of-memory issues.

This file contains a lot of unused data (information for all packages available in Debian), let's keep only used data (i.e. for packages available in Apertis). With this change, the cache file goes from 74 MB to 55 MB.

https://phabricator.apertis.org/T9510

Signed-off-by: Dylan Aïssi dylan.aissi@collabora.com