[Bug] Defaulting lookback to 0 results in consistently incomplete batches

[QMalcolm]

We should switch the default for lookback to 1.

Currently the lookback value defaults to 0. The problem with this is that a lookback of 0 means that the dataset will never have a “complete” batch. This is because when microbatch is run, the current time is used for the latest batch. We do that because we’re favoring freshness over ensuring “only complete batches”. Unfortunately, this combined with lookback=0 makes it such that no batch is ever "complete".

For an example, consider a microbatch model with a batch_size of day, and it's run at noon everyday (12:00:00). If our lookback is 0 then when the microbatch model is run today it’ll get data from today 00:00:00 to 12:00:00. Then tomorrow when my microbatch model it’ll get data for tomorrow 00:00:00 to 12:00:00, but it won’t go back and get the rest of “today’s” data (because the lookback is 0).

Thus the “default” valid behavior should be a lookback of 1. This ensures that batches are complete. The only caveats being when there is regularly late arriving data for which one can set a larger lookback value, or when there is one off late arriving data using —event-time-start + —event-time-end to backfill the specific range.