add label inference support to EncDecSpeakerLabel class
Signed-off-by: nithinraok <nithinrao.koluguri@gmail.com>

# What does this PR do ?

Add label inference support for EncDecSpeakerLabel models

**Collection**: ASR

# Changelog 
- Add new `infer_file` function which returns both logits and embeddings
- update existing `get_embedding` function to use `infer_file`
- add new `get_label` function that returns label automatically (based on trained model labels)
- update existing speaker inference scripts to use these functions

# Usage

* For getting label (for eg: langid)
```python
from nemo.collections.asr.models import EncDecSpeakerLabelModel 
model = EncDecSpeakerLabelModel.from_pretrained('langid_ambernet')
lang = model.get_label(<path_to_audio_file>)
```

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**Pre checks**:
- [ ] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [x] Did you write any new necessary tests?
- [ ] 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