Enable conflict resolution for IRAC state transfer

Current cross-site replication for asynchronous backups overwrites everything in the receiver site. This works fine for active-passive scenarios but IRAC fits active-active scenario better.

We can improve the state transfer by "touching" all keys. IRAC will send them in the background and we can take advantage of conflict resolution.

For performance reasons, we should touch the keys by segments to avoid queueing too many keys in memory.

Also, opens the possibility of automatic state transfer for IRAC.