dht: add hashing and comparison helpers to dht::decorarted_key
dht: add hashing and comparison helpers to dht::decorarted_key

An std::hash specialization, and an equality comparator.

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