Pydantic v2

[mat-sop]

This pr updates version of pydantic to ~2.0.

Changes in generated clients and models:

• parse_obj -> model_validate
• .dict() -> .model_dump()
• Instead of Config class BaseModel uses model_config = ... attribute.
• Refactored validator which handles parsing of custom scalars.
• Upload is no longer dataclass, in v2 pydantic's .model_dump() changes dataclasses to dicts which is harder for client to detect files.
• update_forward_refs -> model_rebuild
• pydantic.json.pydantic_encoder -> pydantic_core.to_jsonable_python
• Optional input fields now have explicit default None value (if schema doesn't specify another) Feature request: set default=None on optional input type fields #165

I see some potential to improve our implementation of custom scalars using some pydantic's v2 features, but this pr is already huge so it aims to sustain the same logic.

resolves #183 #165