Time formats in sinks should be derived from events

It was unclear for me which timestamp is used for making filename. It is not documented anywhere.

My first expectation was to get there timestamp of last event, or maybe timestamp of first event.

But current timestamp is least useful in my point of view — there is a file metadata with creation time. And it doesn't name files as expected when historical data is being processed.

Seems this idea is not new for you https://github.com/timberio/vector/blob/6f290d3e55d78438100b1bd31747c6c4b1630184/src/sinks/aws_s3.rs#L318 but I couldn't find a ticket to track that.