Add deprecation warning for XDCR v1 (CAPI XDCR)

Please add a deprecation warning for CAPI and XDCR v1 to (1) the release notes and (2) the most appropriate XDCR page, probably one of these two:

• http://developer.couchbase.com/documentation/server/4.5/xdcr/xdcr-intro.html
• http://developer.couchbase.com/documentation/server/4.5/xdcr/xdcr-create.html

The CAPI based XDCR will be removed in a future version of Couchbase Server.
 
As far as I know, only the Elasticsearch Connector uses CAPI today (in the form of XDCR v1). There may be some customers who are using it XDCR v1 or CAPI directly, or who do not plan to upgrade their Couchbase Server versions. For these customers, the deprecation warning will give them time to make other plans.
 
The reason for this deprecation is that we have newer protocols that are better supported and we should migrate the ES connector to either DCP or XMEM XDCR (XDCR v2). Deprecating XDCR v1 will allow Couchbase prune code and reduce the surface area that needs to be maintained. There is no plan to remove support for the ES Connector.