added very basic REST API for ldap auth configuration

Change-Id: Iab83ca693516927cb20190d19daf47b8dfede7a4
Reviewed-on: http://review.couchbase.org/44122
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>