Implement ErrorTracker #151
Description
A part of the functionality has been added in #142.
- grouping and summarizing errors is mostly missing
- there doesn't seem to be a good reason for this to be included in the Statistics class
- JS crawlee persists this but doesn't revive it, which is probably a bug
- feat: implement ErrorSnapshotter for error context capture crawlee#2332 exists - should it be ported over?