sstables: define table_subdirectories
sstables: define table_subdirectories

Define a constexpr array of all official table sub-dorectories.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

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