CBD-805: add xperf configs with MAX_CONCURRENT_REPS_PER_DOC=512

Change-Id: Ifa6dee0eba8757c7d1ca74b1976cb846c253d837
Reviewed-on: http://review.couchbase.org/24363
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>