Allow overriding timestamp of event

[yuvipanda]

Very useful when generating eventlog streams from pre-recorded
data.

Fixes #42

[Zsailer]

Thanks, @yuvipanda! This looks great!

Quick follow up question—is it dangerous effect/override timestamps of events? I think, as long as we're not exposing this functionality to operators and users (i.e. through some configurable option etc), it should be safe, right? We don't want people changing timestamps to obfuscate their activity in some way.

[yuvipanda]

https://github.com/yuvipanda/jupyterhub-telemetry-extractor is the code I wrote! Pushes out telemetry logs from parsing JupyterHub logs.

[yuvipanda]

@Zsailer I don't think this PR changes our security posture. For examples, admins can put in loggers with custom handlers that can change timestamps (or any other data) as they wish. If users are running code in the same python process (as we do with notebooks most of the time), they can also monkeypatch easily to do the same thing. So we should continue treating all telemetry from user created processes as untrusted, regardless of what happens with this PR...

[Zsailer]

we should continue treating all telemetry from user created processes as untrusted

👍 Sounds good. This looks good to me!