vad infer refactor
1. Organize and move parameters used in `vad_infer.py` to _yaml_ config file` conf/vad_inference_postprocessing.yaml`.
2. Add gen_overlap_seq, gen_seg_table and write_to_manifest choice to `vad_infer.py` so the script can cover the whole pipeline from 
**frame -> overlapped smoothing filter -> write to rttm-like table -> write to manfiest json file (for possible next step)** instead of using multiple scripts as in previous.
3. Remove duplicate code in  `vad_overlap_posterior.py`  and  `write_long_audio_manifest.py`  in scripts/voice_activity_detection.
4. Reflect updates in `tutorials/asr/Online_Offline_Microphone_VAD_Demo.ipynb ` and `tutorials/asr/Voice_Activity_Detection.ipynb`
5. bugfix for diarization yaml file about input data example.
6. Unify and rename _window_length_in_sec_ and _shift_length_in_sec_ across files to reduce confusion.