message: Use env var to set min non-trivial nodes
  Add support to use the environment variable TF_OV_MIN_NONTRIVIAL_NODES to set the cluster threshold for an encapsulated nGraph cluster. A cluster is busted if the number of non-trivial nodes (excluding Const and Identity) exceed the specified minimum number of non-trivial nodes.
diff: @@ -51,8 +51,6 @@ namespace ngraph_bridge {
  // NGRAPH_TF_DISABLE_DEASSIGN_CLUSTERS=1.
  //
  -static const int MIN_NONTRIVIAL_NODES = 6;
  -
  unordered_map<string, int> deassigned_histogram;
  int num_nodes_marked_before_deassign = 0;
  @@ -189,7 +187,14 @@ Status DeassignClusters(Graph* graph) {
  }
  }
  - if (non_trivial_count < MIN_NONTRIVIAL_NODES) {
  + int min_non_trivial_nodes = 6;
  + if (std::getenv("TF_OV_MIN_NONTRIVIAL_NODES") != nullptr) {
  + min_non_trivial_nodes =
  + std::stoi(std::getenv("TF_OV_MIN_NONTRIVIAL_NODES"));
  + }
  + NGRAPH_VLOG(1) << "MIN_NONTRIVIAL_NODES set to " << min_non_trivial_nodes;
  +
  + if (non_trivial_count < min_non_trivial_nodes) {
  NGRAPH_VLOG(2) << "Busting cluster " << cluster_idx;
  for (auto node : nodes) {
  NGRAPH_VLOG(2) << "Busting node: " << node->name() << " ["
  