Disable failing when not all creator properties are known

Move CheckpointStatsCache out of legacy package; Remove unused CheckpointingStatistics#generateCheckpointStatistics method

Remove JsonInclude.Include.NON_NULL from CheckpointStatistics; Pull null check out of CheckpointStatistics#generateCheckpointStatistics; Make CheckpointStatistics#checkpointStatisticcsPerTask non nullable; Add fail on missing creator property

This closes #4763.