sstables: index_reader: Introduce advance_and_check_if_present()
sstables: index_reader: Introduce advance_and_check_if_present()

duarten/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla