Realtime to Offline segment conversion: Provision for rolling offline segments based on segment size

REALTIME tables segment size can be controlled using `realtime.segment.flush.threshold.segment.size` (say "100M")
We don't have any similar configuration for OFFLINE tables which can be used during Realtime to Offline table conversion.

There is a configuration `maxNumRecordsPerSegment` with which we can indirectly achieve desired size. However, having a direct size based control will be really helpful and straight forward.

Start by tracing the realtime-to-offline table conversion and the existing maxNumRecordsPerSegment configuration. Compare that path with the realtime.segment.flush.threshold.segment.size setting, then verify that offline conversion supports a direct segment-size control and that the resulting segments follow the configured limit.

Written by the indexing model from the issue text.