chanserv: SET SIGNKICK and PRIVATE (typed channel settings)

Introduce a typed ChanSettings struct + ChanSetting enum for ChanServ's on/off
options instead of a bag of string flags, so a new option is one field and the
compiler proves every site handles it. First two, both functional: SIGNKICK
attributes ChanServ kicks with who requested them; PRIVATE hides the channel
from LIST. Folded through the event log like the other channel state (node-local,
no gossip), shown in INFO. One ChannelSettingsSet event, one Store method.

src/grpc.rs

@@ -129,7 +129,8 @@ fn to_wire(entry: &LogEntry) -> Option<ReplicationEvent> {
         | Event::ChannelAccessDel { .. }
         | Event::ChannelAkickAdd { .. }
         | Event::ChannelAkickDel { .. }
-        | Event::ChannelEntryMsgSet { .. } => return None,
+        | Event::ChannelEntryMsgSet { .. }
+        | Event::ChannelSettingsSet { .. } => return None,
     };
     Some(ReplicationEvent { origin: entry.origin().to_string(), seq: entry.seq(), lamport: entry.lamport(), kind: Some(kind) })
 }