Feature request: additional precision for log timestamps

It seems current log lines add timestamps with second-level precision. In our logging infra this results in thousands of logs sharing the same timestamp which hurts our ability to look at the order of logs. One can drill down on log specific, precise timestamps as infra allows but this loses ordering between log types still.

Open to a PR flipping on precise timestamps? Was this left at the current precision intentionally perhaps?

From what I read logrus accepts go `time` formats, so setting `TimestampFormat` to `time.RFC3339Nano` could be nice, which would provide nanosecond level timestamps.