CBIDXT-16: protobuf definitions.

between query and indexer.

Change-Id: Iefaa356617ef52a3cfe51483b9d07551330b575b
Reviewed-on: http://review.couchbase.org/41172
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>