When started the sstable_directory is constructed with a bunch of booleans that control the way its process_sstable_dir method works. It's shorter and simpler to pass these booleans into method directly, all the more so there's another flag that's already passed like this.
Closes#12005
* github.com:scylladb/scylladb:
sstable_directory: Move all RAII booleans onto flags
sstable_directory: Convert sort-sstables argument to flags struct
sstable_directory: Drop default filter