[TTS] Append pretrained FastPitch & SpectrogamEnhancer pair to available models
# What does this PR do ?

Add aliases for pretrained English FastPitch and SpectrogramEnhancer models (already published on NGC)
https://catalog.ngc.nvidia.com/orgs/nvidia/teams/nemo/models/tts_en_fastpitch_spectrogram_enhancer_for_asr_finetuning

Will be used in upcoming ASR-TTS tutorial.

**Collection**: TTS

# Changelog 
- Add `tts_en_fastpitch_for_asr_finetuning` model to list of FastPitch models
- Add `tts_en_spectrogram_enhancer_for_asr_finetuning` model to list of SpectrogramEnhancer models

# Usage
```python
import nemo
from nemo.collections.tts.models import FastPitchModel, SpectrogramEnhancerModel

fastpitch = FastPitchModel.from_pretrained(model_name="tts_en_fastpitch_for_asr_finetuning")
enhancer = SpectrogramEnhancerModel.from_pretrained(model_name="tts_en_spectrogram_enhancer_for_asr_finetuning")

```

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**PR Type**:
- [ ] New Feature
- [ ] Bugfix
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## Who can review?

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# Additional Information
* Related to #6955 
