Model.findById - Read from Replica

Enhance model methods backed by KV operations to support reading from replicas

Model.findById uses `collection.get(key);` under the hood which fetches the document from Couchbase datastore's active node.
We need to enhance this by adding a findOption `replica` by default replica will be fault (the behavior that exists today) but when set to true findById should be able to attempt to get a document from the replica in lieu of document not found in the active node.