MB-12750 proxy remote cluster rest api to goxdcr

the following api's

- GET  /pools/default/remoteClusters
- POST /pools/default/remoteClusters
- POST /pools/default/remoteCluster/Id
- DELETE  /pools/default/remoteCluster/Id

Change-Id: I49ec3039397912793b113e478b5e45d3fd10bacb
Reviewed-on: http://review.couchbase.org/44296
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>