XDCR to support retrieve collection manifest over SSL

In a potential cloud set up, it's possible to have permission given the remote cluster reference for replication to target KV, but not have permission to contact remote cluster ns_server to retrieve a collections manifest.

2020-08-27T15:54:38.406-07:00 ERRO GOXDCR.Utils: Failed to get manifest for bucket 'couchbasecloudbucket'. host=cb-0002.ead75783-adbe-42ac-8937-e187da9abf80.dp.cloud.couchbase.com:18091, err=<nil>, statusCode=403

XDCR needs to properly handle this error (by disabling collections replication) and raise warning to indicate that manual intervention is required on the target side.

EDIT - there's possibility that this the collection manifest needs to be retrieved with SSL credentials...
EDIT - the log msg above is from a target cluster of 6.5.1