The object in question fully describes the keyspace to be created and,
among other things, contains replication strategy options. Next patches
move the "initial_tablets" option out of those options and keep it
separately, so the ks metadata should also carry this option separately.
This patch is _just_ extending the metadata creation API, in fact the
new field is unused (write-only) so all the places that need to provide
this data keep it disengaged and are explicitly marked with FIXME
comment. Next patches will fix that.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>