The `nomad operator raft logs` command uses a raft helper that reads
in the logs from raft and serializes them to JSON. The previous
implementation returned the slice of all logs and then serializes the
entire object. Update the helper to stream the log entries and then
serialize them as newline-delimited JSON.
The `nomad operator raft` and `nomad operator snapshot state`
subcommands for inspecting on-disk raft state were hidden and
undocumented. Expose and document these so that advanced operators
have support for these tools.
