velia: Use journald for logging

Current logging sink duplicates information like time and severity into
the journald which is not desirable. Use journald logging sink and
journald's capabilities if possible like in cla-sysrepo.

This code comes from cla-sysrepo,
commit 1d4aa45353f8e52dda29a8d5b453745c58c80913.

Change-Id: Ic4ae748d07edb4daa4ef0c15c3f8aab42fd8482e
diff --git a/src/utils/journal.h b/src/utils/journal.h
new file mode 100644
index 0000000..499046e
--- /dev/null
+++ b/src/utils/journal.h
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2016-2019 CESNET, https://photonics.cesnet.cz/
+ *
+ * Written by Jan Kundrát <jan.kundrat@cesnet.cz>
+ *
+*/
+
+#pragma once
+
+#include <memory>
+
+namespace spdlog {
+namespace sinks {
+class sink;
+}
+}
+
+namespace velia::utils {
+bool isJournaldActive();
+std::shared_ptr<spdlog::sinks::sink> create_journald_sink();
+}