sstables: enable token monotonicity validation by default
sstables: enable token monotonicity validation by default

Partition key order validation in data written to sstables can be very
disruptive. All our components in the storage layers assume that
partitions are in order, which means that reading out-of-order
partitions triggers undefined behaviour. Computer scientists often joke
that undefined behaviour can erase your hard drive and in this case the
damage done by undefined behaviour caused by out-of-order partitions is
very close to that. The corruption is known to mutate causing crashes,
corrupting more data and even loose data. For this reason it is
imperative that out-of-order partitions cannot get into sstables. This
patch enables token monotonicity validation unconditionally in
the sstable writer. As partition key monotonicity checks involve a key
copy per partition, which might have an impact on the performance, we do
the next best thing instead and enable only token monotonicity
validation.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla