examples : add VAD speech segments example (#3147)

This commit adds an example that demonstrates how to use a VAD (Voice
Activity Detection) model to segment an audio file into speech segments.

Resolves: https://github.com/ggml-org/whisper.cpp/issues/3144

examples/CMakeLists.txt

@@ -105,6 +105,7 @@ else()
     add_subdirectory(bench)
     add_subdirectory(server)
     add_subdirectory(quantize)
+    add_subdirectory(vad-speech-segments)
     if (WHISPER_SDL2)
         add_subdirectory(stream)
         add_subdirectory(command)