MB-10721 attach ns_server-ui header to every request issued by ui

convenient for any ui specific customizations in rest api

Change-Id: I884b09eb7cb4ba4c8695ed5043c4c021b21d05a4
Reviewed-on: http://review.couchbase.org/36119
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>