multi: add remote RPC signing wallet implementation

sample-lnd.conf

@@ -1178,6 +1178,23 @@ litecoin.node=ltcd
 ; rpcmiddleware.addmandatory=my-example-middleware
 ; rpcmiddleware.addmandatory=other-mandatory-middleware
 
+[remotesigner]
+
+; Use a remote signer for signing any on-chain related transactions or messages.
+; Only recommended if local wallet is initialized as watch-only. Remote signer
+; must use the same seed/root key as the local watch-only wallet but must have
+; private keys.
+; remotesigner.enable=true
+
+; The remote signer's RPC host:port.
+; remotesigner.rpchost=remote.signer.lnd.host:10009
+
+; The macaroon to use for authenticating with the remote signer.
+; remotesigner.macaroonpath=/path/to/remote/signer/admin.macaroon
+
+; The TLS certificate to use for establishing the remote signer's identity.
+; remotesigner.tlscertpath=/path/to/remote/signer/tls.cert
+
 [bolt]
 
 ; If true, prevents the database from syncing its freelist to disk.