message: add debug log
  Adds a debug log line when a cluster is skipped from CDS response.
  Risk Level: Low (debug logging)
  Testing: N/A
  Docs Changes: N/A
  Release Notes: N/A
diff: @@ -77,6 +77,8 @@ void CdsApiImpl::onConfigUpdate(
  if (cm_.addOrUpdateCluster(cluster, resource.version())) {
  any_applied = true;
  ENVOY_LOG(debug, "cds: add/update cluster '{}'", cluster.name());
  + } else {
  + ENVOY_LOG(debug, "cds: add/update cluster '{}' skipped", cluster.name());
  }
  } catch (const EnvoyException& e) {
  exception_msgs.push_back(fmt::format("{}: {}", cluster.name(), e.what()));
  