XDCR: Allow filtering out of expiry messages to save overhead

Once document expirations in DCP are utilising the specific DCP Expire (0x59) opcode rather than the DCP Delete (0x58) opcode, as per MB-26907, it might be useful in certain use-cases to not replicate document expiration to a remote cluster over XDCR.

In these use-cases where users create a high number of short-lived documents, they will also generate an equally-frequent series of document expiration events. This expiration will be optimistically sent to the remote cluster, where it then then be sent onwards via XDCR including returning the mutation back to the original source cluster in the case of simple 2-cluster bidirectional XDCR.

As the document creation will be passed to the remote cluster as a Set_with_Meta operation, the expiry time will be transferred with the document in its metadata. Therefore transmitting document expiries might be considered excessive overhead as the documents would naturally expire on the target cluster anyway.

If the user wishes, they could filter out these expirations on the understanding that the document will be expired on a different schedule, but with the saving of this additional round trip traffic.