DR Auto-Sync: add a flag in DR_STATE file to indicate whether the DR replica is (ACID) recoverable or not

in current design, we need to keep the config item `pause-region-split` to `true` to ensure the DR replica is (ACID) recoverable, it means the administrator need to know this information before disaster recovery.
it may help if we add a flag in DR_STATE file to mark if this config item keeps being `true` since the last time of `async` state