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/vad-speech-segments/README.md

@@ -0,0 +1,52 @@
+# whisper.cpp/examples/vad-speech-segments
+
+This examples demonstrates how to use a VAD (Voice Activity Detection) model to
+segment an audio file into speech segments.
+
+### Building the example
+The example can be built using the following command:
+```console
+cmake -S . -B build
+cmake --build build -j8 --target vad-speech-segments
+```
+
+### Running the example
+The examples can be run using the following command, which uses a model
+that we use internally for testing:
+```console
+./build/bin/vad-speech-segments \
+    -vad-model models/for-tests-silero-v5.1.2-ggml.bin \
+    --file samples/jfk.wav \
+    --no-prints
+
+Detected 5 speech segments:
+Speech segment 0: start = 0.29, end = 2.21
+Speech segment 1: start = 3.30, end = 3.77
+Speech segment 2: start = 4.00, end = 4.35
+Speech segment 3: start = 5.38, end = 7.65
+Speech segment 4: start = 8.16, end = 10.59
+```
+To see more output from whisper.cpp remove the `--no-prints` argument.
+
+
+### Command line options
+```console
+./build/bin/vad-speech-segments --help
+
+usage: ./build/bin/vad-speech-segments [options] file
+supported audio formats: flac, mp3, ogg, wav
+
+options:
+  -h,        --help                          [default] show this help message and exit
+  -f FNAME,  --file FNAME                    [       ] input audio file path
+  -t N,      --threads N                     [4      ] number of threads to use during computation
+  -ug,       --use-gpu                       [true   ] use GPU
+  -vm FNAME, --vad-model FNAME               [       ] VAD model path
+  -vt N,     --vad-threshold N               [0.50   ] VAD threshold for speech recognition
+  -vspd N,   --vad-min-speech-duration-ms  N [250    ] VAD min speech duration (0.0-1.0)
+  -vsd N,    --vad-min-silence-duration-ms N [100    ] VAD min silence duration (to split segments)
+  -vmsd N,   --vad-max-speech-duration-s   N [FLT_MAX] VAD max speech duration (auto-split longer)
+  -vp N,     --vad-speech-pad-ms           N [30     ] VAD speech padding (extend segments)
+  -vo N,     --vad-samples-overlap         N [0.10   ] VAD samples overlap (seconds between segments)
+  -np,       --no-prints                     [false  ] do not print anything other than the results
+```