feat: implement montauk::service_log & add support to system services

programs/include/montauk/service_log.h

@@ -0,0 +1,24 @@
+/*
+ * service_log.h
+ * Common logging policy for MontaukOS userspace services.
+ */
+
+#pragma once
+
+#include <montauk/syscall.h>
+
+namespace montauk {
+
+// Append one newline-free message to the system log. When the service was
+// launched from a userspace terminal, echo the same message there as well.
+inline void service_log(const char* message) {
+    if (message == nullptr) return;
+
+    write_log(message);
+    if (terminal_attached()) {
+        print(message);
+        print("\n");
+    }
+}
+
+}