Add new pretrained Spanish ASR models
Signed-off-by: Elena Rastorgueva <erastorgueva@nvidia.com>

# What does this PR do ?
Add new pretrained Spanish ASR models (Citrinet 1024, Conformer CTC Large, Conformer Transducer Large, ContextNet 1024) to `list_available_models` and to documentation

**Collection**: [Note which collection this PR will affect]
ASR

# Changelog 
* Add new pretrained Spanish ASR models (Citrinet 1024, Conformer CTC Large, Conformer Transducer Large, ContextNet 1024) to the method `list_available_models` in `EncDecCTCModelBPE` and `EncDecRNNTBPEModel`.
* Added the 4 models also to the list of Spanish ASR models in the documentation. 

# Usage


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- [n/a] Did you write any new necessary tests?
- [y] Did you add or update any necessary documentation?
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**PR Type**:
- [y] New Feature
- [ ] Bugfix
- [y] Documentation

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# Additional Information
* Related to # (issue)
