Reduce the frequency of state file creation during data growth

While data load is ongoing, the state file creation is very aggressive. The state file number reaches to 4000+ in seconds. Checkpointing policy can be improved to add a minimum limit of at least few seconds to min.

magma_bench /data/single --kvstore 1 --ndocs 5200000 --nwrites 5200000 --nwriters 1 --batch-size 10 --memquota 10000000 --vallen 1024 --benchmark writeSequential --engine-config '

{"enable_lookup_on_set":true, "enable_directio":false, "enable_wal":true, "max_checkpoints":5}

' --engine magma --stats stats.json --active-stats