Add scikit-learn to project.toml

[NoB0]

Cannot use cosine NLU, see trace:

Traceback:
../../miniconda3/envs/usersimcrs/lib/python3.11/importlib/__init__.py:126: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
tests/simulator/agenda_based/test_interaction_model.py:8: in <module>
    from dialoguekit.utils.dialogue_reader import json_to_dialogues
../../miniconda3/envs/usersimcrs/lib/python3.11/site-packages/dialoguekit/utils/__init__.py:4: in <module>
    from dialoguekit.utils.dialogue_evaluation import Evaluator
../../miniconda3/envs/usersimcrs/lib/python3.11/site-packages/dialoguekit/utils/dialogue_evaluation.py:11: in <module>
    from dialoguekit.nlu.models.satisfaction_classifier import (
../../miniconda3/envs/usersimcrs/lib/python3.11/site-packages/dialoguekit/nlu/__init__.py:9: in <module>
    from dialoguekit.nlu.models.intent_classifier_cosine import (
../../miniconda3/envs/usersimcrs/lib/python3.11/site-packages/dialoguekit/nlu/models/intent_classifier_cosine.py:7: in <module>
    from sklearn.feature_extraction.text import TfidfVectorizer
E   ModuleNotFoundError: No module named 'sklearn'