fix bug in intent/slot model reloading
Signed-off-by: Carol Anderson <carola@nvidia.com>

# What does this PR do ?

Addresses the problem raised in #2769, where models cannot be reloaded if the data directory specified in the config is missing, such as when a model is reloaded on a different machine from the one on which it was trained.

**Collection**: NLP

# Changelog 
- Added a line to the IntentSlotClassificationModel and MultiLabelIntentSlotClassificationModel `__init__` methods to check whether `_is_model_being_restored()` is False before setting it to True. 
- Also fixed minor errors in the Zero Shot Intent Recognition model code: changed the display name of the tutorial notebook and corrected an incorrect type hint in the inference dataset class. 

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**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

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# Additional Information
* Related to  #2769 
