Save the timestamp of when Telemetry emits the event and use that when sending to Logflare

[chasers]

Currently the timestamp used for the Telemetry event is based on when the event is ingested into Logflare because the timestamp key is not present with each event as they come over. We want to save the timestamp when Logflare Telemetry first sees the event so we know exactly when that event was emitted.