Support disallow_untyped_decorators = false option for 3rd party libraries #9442

Feature

Support disallow_untyped_decorators option for 3rd party libraries
Example:

[mypy-pytest-asyncio]
disallow_untyped_decorators = false

Pitch

Example
pytest decorators are widely used in the testing of Python code. pytest is still untyped for now.
It would be nice to have the possibility to check the typing of own decorators but ignore untyped decorators of some 3rd party libraries.