This is an implementation of `raft::failure_detector` for Scylla that uses gms::gossiper to query `is_alive` state for a given raft server id. Server ids are translated to `gms::inet_address` to be consumed by `gms::gossiper` with the help of `raft_rpc` class, which manages the mapping. Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com> Message-Id: <20210129223109.2142072-1-pa.solodovnikov@scylladb.com>