Motivation

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1. Checks metadata (mappings, binary_meta, caches - can check inside Ignite, not reading files), prepare updates if any.
2. Polls the Queue, transforms ReadSegment data to Iterator<CdcEvent>, pushes them to CdcConsumer.
3. If CdcConsumer#onEvents returns true:
   1. Persists CdcConsumerState.
   2. Write RealtimeCdcRecord record to WAL with the WALPointer.
4. Optimization: transform segment buffers to CdcEvents in background (to reduce the buffer usage). CdcConsumer should be async then?

Try restart Ignite's internal CDC processswitch to the realtime mode:

1. User sends the command to switch modes
2. Ignite does initialization - CdcWorker, buffer
3. Writes TryStartRealtimeCdcRecord into WAL and rollover current segment(since this record realtime cdc becomes active again).
4. Ignite monitors the CDC directory, awaits while segment with the record cleaned - it means ignite-cdc.sh reach the record and stops capturing the data.
5. If buffer is not overflowed in this moment - Ignite enables CDCConsumer and starts sending the records
6. Otherwise, ordinal stop is invoked (with writing StopRealtimeCdc record)

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