[TTS] Support speaker level pitch normalization
# What does this PR do ?

Add script for computing speaker specific pitch mean & standard deviation, and logic in data loader to use it at training time.

Global pitch normalization can be done using the previous configs, or by providing a JSON with only a "default" key.

There is a bit of awkward typing logic due to our speaker IDs being integers but JSON only supporting string keys.

**Collection**: [TTS]

# Changelog
- Add script for computing the mean and standard deviation of pitch for each speaker in a dataset and storing it in a JSON dictionary
- Add data loading logic to support parsing these pitch statistics from the JSON.
- Register stats file in FastPitch model
- Add pitch stats for Spanish openSLR data and modify .yaml config example.
- Added map from speaker name to speaker ID (integer) used as the keys in the pitch statistics, and as the possible inputs to the NGC model (https://catalog.ngc.nvidia.com/orgs/nvidia/teams/nemo/models/tts_es_multispeaker_fastpitchhifigan). The script for creating this speaker mapping will not be merged until I add the script/tutorial for downloading and processing the openSLR data.

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- [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?
- [ ] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
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**PR Type**:
- [x] New Feature
- [ ] Bugfix
- [ ] Documentation
