cmd/lncli: add new exportchanbackup and restorechanbackup cli commands

In this commit, we add two new cli commands: exportchanbackup and
restorechanbackup. These two commands allow users to export backups
(single or multi) for one or all channels, and also restore these
backups (single or multi) from a file to attempt to recover the
channels.

Additionally, we extend the `lncli create` call to also accept these
backups so users can have a single command to restore both their
on-chain and off-chain funds.

cmd/lncli/main.go

@@ -295,6 +295,8 @@ func main() {
 		feeReportCommand,
 		updateChannelPolicyCommand,
 		forwardingHistoryCommand,
+		exportChanBackupCommand,
+		restoreChanBackupCommand,
 	}
 
 	// Add any extra autopilot commands determined by build flags.