Refactor/unify ASR offline and buffered inference
Signed-off-by: fayejf <fayejf07@gmail.com>

# What does this PR do ?

Refactor/unify ASR offline and buffered inference

**Collection**: ASR

# Changelog 
1. Clean `transcribe_speech.py` by moving resuable functions to `trancribe_utils.py`
2. Unify `speech_to_text_buffered_infer_rnnt.py` and `speech_to_text_buffered_infer_ctc.py` to have the same input format and behavior as `transcribe_speech.py` including 

> 1. Unify the input format and inconsistent variable names such as `chunk_len_in_secs` and `chunk_len_in_ms`
> 2. support no groundtruth 'txt' condition and audio_dir condition, 
> 3. Modify and move `get_wer_feat` in  `speech_to_text_buffered_infer_rnnt.py` and `get_wer_feat` in  `speech_to_text_buffered_infer_ctc.py` to  `get_buffered_pred_feat_rnnt` and `get_buffered_pred_feat` in `transcribe_utils.py `
> 4. remove WER calculation in above scripts.
> 5. Write all information presented in input manifest to output manifest.

# Usage
* See headers in each example scripts

# Before your PR is "Ready for review"
**Pre checks**:
- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [x] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [x] New Feature
- [ ] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


## Who can review?

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

# Additional Information
* Related to # (issue)
