Reduce log-level of "Offline-mode header not found"

This particular log is not very useful for the average user.
Reduce the log-level to avoid possible confusion.

Related-to: TOR-2277

Signed-off-by: Jeremias Cordoba <jeremias.cordoba@toradex.com>

src/torizon_virtual_secondary/dockerofflineloader.cc

@@ -666,7 +666,7 @@ void DockerComposeFile::backwardTransform() {
   if (compose_lines_.size()) {
     const std::string first_line = compose_lines_.front();
     if (! std::regex_match(first_line, offline_mode_header_re)) {
-      LOG_INFO << "Offline-mode header not found: skipping backward transform";
+      LOG_DEBUG << "Offline-mode header not found: skipping backward transform";
       return;
     }
   }