Add: Notebook for custom model api

[chakravarthik27]

Description

This pull request implements a significant enhancement in the notebook functionality, introducing support for a custom hub. The addition of this feature enables users to seamlessly integrate and leverage personalized nlp models within the notebook environment.

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➤ Fixes # (issue)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

Usage

Let's do with Langtest

harness = Harness(task="text-classification",
                  model={'model': model, "hub": "custom"}, data={'data_source': 'path/to/data/imdb.csv'})

Checklist:

• I've added Google style docstrings to my code.
• I've used pydantic for typing when/where necessary.
• I have linted my code
• I have added tests to cover my changes.

Screenshots (if appropriate):