walletrpc+subserver_config: add coin selection strategy

With this commit we also add the config-level coin selection strategy to
the wallet RPC server.

subrpcserver_config.go

@@ -197,6 +197,11 @@ func (s *subRPCServerConfigs) PopulateDependencies(cfg *Config,
 			subCfgValue.FieldByName("CurrentNumAnchorChans").Set(
 				reflect.ValueOf(cc.Wallet.CurrentNumAnchorChans),
 			)
+			subCfgValue.FieldByName("CoinSelectionStrategy").Set(
+				reflect.ValueOf(
+					cc.Wallet.Cfg.CoinSelectionStrategy,
+				),
+			)
 
 		case *autopilotrpc.Config:
 			subCfgValue := extractReflectValue(subCfg)