Pass timestamps from the clients for non-realtime/batch processed data

[Tannergoods]

@timgl this request came via @sixteenmillimeter

"is there a way to migrate data from other platforms or pass timestamps from the clients for non-realtime/batch processed data?"

[timgl]

You can already do this! I've updated the API to reflect how to do that. https://github.com/PostHog/posthog/wiki/API