fix(event-handler): replace Optional[X] and List[X] with X | None and list[X] in openapi/models.py

Replace deprecated typing aliases with modern Python 3.10+ syntax:
- Optional[X] -> X | None
- List[X] -> list[X]
- Dict[X, Y] -> dict[X, Y]
- Set[X] -> set[X]
- Remove unused imports: Dict, List, Optional, Set from typing

Part of #8088

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

Author: hirenkumar-n-dholariya