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>

sample-lnd.conf

@@ -589,6 +589,15 @@
 ; pong failure.
 ; no-disconnect-on-pong-failure=false
 
+; 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.
+; upfront-shutdown-address=
+
+
 [fee]
 
 ; Optional URL for external fee estimation. If no URL is specified, the method