filesystem monitor: auto-adjust package update interval based on performance

That way, it can schedule big dropboxes to be updated more slowly, thus not slowing down the queue for everyone

Start by locating the filesystem monitor and the code that schedules package updates and feeds the queue. Clarify how performance should be measured and how large Dropbox workloads should be identified. Done means update intervals adjust without slowing the shared queue, with behavior verified by the project's available tests or monitoring.

Written by the indexing model from the issue text.