Related to #5898, this reports an anonymized summary of errors stored in Redis into the analytics payload.
For each error stored, this includes:
- A `count` attribute with the number of occurrences of the error
- A `loc` attribute with the 3 topmost lines in the stack trace. Note that stack traces only contain package name + line number (example: github.com/fleetdm/fleet/server.go:12
This also includes a minor refactor around error types.
