refactor: add unified gatherArgument helper for request parsing

pipeline-runner/src/messageutils.cpp

@@ -28,4 +28,11 @@ PIHTTP::MessageMutable noContent() {
 	return msg;
 }
 
+PIString gatherArgument(const PIHTTP::MessageConst & request, const PIString & key) {
+	PIJSON js = PIJSON::fromJSON(PIString::fromUTF8(request.body()));
+	if (js.contains(key)) return js[key].toString();
+	if (request.arguments().contains(key)) return request.arguments().value(key);
+	return {};
+}
+
 } // namespace MessageUtils