sstables/sstables.hh is one of our heaviest headers and it's better that we don't
include it if possible. For some users, like distributed_loader, we are mostly
interested in knowing the shape of structures used to open an SSTable.
They are:
- the entry_descriptor, representing an SSTable that we are scanning on-disk
- the sstable_open_info, representing information about a local, opened SSTable
- the foreign_sstable_open_info, representing information about an opened SSTable
that can cross shard boundaries.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
