There are two of those -- the POST /storage_service/keyspace that loads
and streams new sstables from /upload and POST /storage_service/restore
that does the same, but gets sstables from object store.
The new optional parameter allow users to tun the streaming phase
behavior. The test/pylib client part is also updated here.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>