Rename config vars. Add widget holder template and endpoint to serve it. Add dockerfile

internal/service/yookassa/config/yookassa.go

@@ -13,8 +13,9 @@ type YooKassa struct {
 
 	ApiBaseKey       string
 	ApiBaseSecret    string
-	ApiPaymentKey    string
-	ApiPaymentSecret string
+	ApiPayoutKey    string
+	ApiPayoutSecret string
+	WidgetVersion    string
 
 	CallbackProcessTimeout time.Duration
 }