Support Agglomerative clustering. (#1384)

We use the open-source implementation from
https://github.com/cdalitz/hclust-cpp

sherpa-onnx/csrc/fast-clustering-config.h

@@ -0,0 +1,28 @@
+// sherpa-onnx/csrc/fast-clustering-config.h
+//
+// Copyright (c)  2024  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_FAST_CLUSTERING_CONFIG_H_
+#define SHERPA_ONNX_CSRC_FAST_CLUSTERING_CONFIG_H_
+
+#include <string>
+
+#include "sherpa-onnx/csrc/parse-options.h"
+
+namespace sherpa_onnx {
+
+struct FastClusteringConfig {
+  // If greater than 0, then threshold is ignored
+  int32_t num_clusters = -1;
+
+  // distance threshold
+  float threshold = 0.5;
+
+  std::string ToString() const;
+
+  void Register(ParseOptions *po);
+  bool Validate() const;
+};
+
+}  // namespace sherpa_onnx
+#endif  // SHERPA_ONNX_CSRC_FAST_CLUSTERING_CONFIG_H_