Consolidate sgr and cbl replication stats

Existing CBL replication stats assume that all replications with the local SG as the passive peer are CBL replications. In 2.8.0, these may also be sg-replicate2 replications running on remote nodes.

In addition, there is duplicate counting happening for CBL replication stats and sg-replicate2 stats. Since replication is symmetrical, the same event needs to be reported differently based on the replication type. e.g. handleRev as the passive peer represents a document being pushed to the node, while handleRev as the active peer represents a document being pulled by the node.

We want to minimize performance overhead associated with stat collection, so need to review the approach taken to ideally come up with a generic collection approach that can be reused for both CBL replication stats, sg-replicate passive stats, and sg-replicate active stats.