examples : fix and improv docs for the grammar generator (#4909)

* Create pydantic-models-to-grammar.py

* Added some comments for usage

* Refactored Grammar Generator

Added example and usage instruction.

* Update pydantic_models_to_grammar.py

* Update pydantic-models-to-grammar-examples.py

* Renamed module and imported it.

* Update pydantic-models-to-grammar.py

* Renamed file and fixed grammar generator issue.

* Fixed some issues and bugs of the grammar generator. Imporved Documentation

* Update pydantic_models_to_grammar.py