Reduce size of cache file to avoid OOM issue

Changes of this MR:

• Add an option allowing to disable the cache for packaging-data-fetch-downstream. If the oom issue happens again, dashboard users have a way to update the dashboard anyway.
• Check only for active descendant branches. Branches not used anymore are ignored and not stored in the cache file to reduce its size.

To determine if removing unused branches is enough to avoid the oom issue, the cache file need to be regenerated.

https://phabricator.apertis.org/T9440