multi: add new config option upfront-shutdown-address

Introduced a new config value `upfront-shutdown-address`
in the `lnd.conf` file. This ensures that channel close
funds are transferred to the specified shutdown address.
The value applies to both the funder and the fundee but
can be overridden by the value specified during
`openchannel` or by the `channel acceptor`.

NOTE: If this field is set when opening a channel with a
peer that does not advertise support for upfront shutdown
feature, the channel open will fail.

Signed-off-by: Nishant Bansal <nishant.bansal.282003@gmail.com>

config.go

@@ -537,6 +537,15 @@ type Config struct {
 	// NoDisconnectOnPongFailure controls if we'll disconnect if a peer
 	// doesn't respond to a pong in time.
 	NoDisconnectOnPongFailure bool `long:"no-disconnect-on-pong-failure" description:"If true, a peer will *not* be disconnected if a pong is not received in time or is mismatched. Defaults to false, meaning peers *will* be disconnected on pong failure."`
+
+	// UpfrontShutdownAddr specifies an address that our funds will be paid
+	// out to on cooperative channel close. This applies to all new channel
+	// opens unless overridden by an option in openchannel or by a channel
+	// acceptor.
+	// Note: If this field is set when opening a channel with a peer that
+	// does not advertise support for the upfront shutdown feature, the
+	// channel open will fail.
+	UpfrontShutdownAddr string `long:"upfront-shutdown-address" description:"The address to which funds will be paid out during a cooperative channel close. This applies to all channels opened after this option is set, unless overridden for a specific channel opening. Note: If this option is set, any channel opening will fail if the peer does not explicitly advertise support for the upfront-shutdown feature bit."`
 }
 
 // GRPCConfig holds the configuration options for the gRPC server.