In some scenario in our cluster, we may want delta streamer to slow down a bit.
so it's nice to have a parameter to control the min sync interval of each sync in continuous mode.
this param is default to 0, so this should not affect current logic.
minor pr: #921
the main reason we want to slow it down is that aws s3 is charged by s3 get/put/list requests. we don't want to pay for too many requests for a really slow change table.