looprpc: deposit outpoints for QuoteRequest

This commit adds static address deposit outpoints to the
QuoteRequest message. It allows to quote for loop in swaps
with the total value of specified deposits.

Author: hieblmi

looprpc/client.proto

@@ -760,6 +760,13 @@ message QuoteRequest {
     probing and payment.
     */
     bool private = 7;
+
+    /*
+    Static address deposit outpoints that will be quoted for. This option only
+    pertains to loop in swaps. Either this or the amt parameter can be set at
+    the same time.
+    */
+    repeated string deposit_outpoints = 8;
 }
 
 message InQuoteResponse {