feature(lightweight transactions): change CL for writes
feature(lightweight transactions): change CL for writes

By Kostya'a request: it's not nesessary to load data with CL=SERIAL, it only slows things down.
You can load with any CL but test with SERIAL

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests