This PR marks system_replicated_keys as a system keyspace. It was missing when the keyspace was added. A side effect of that is that metrics that are not supposed to be reported are. Fixes #27903 Closes scylladb/scylladb#27954 * github.com:scylladb/scylladb: distributed_loader: system_replicated_keys as system keyspace replicated_key_provider: make KSNAME public