Describe the bug
If you use the PyCharm-provided auto-completion in a model config, this produces a SyntaxError in the code as the import for Extra is missing.

To Reproduce

class M(pydantic.BaseModel):
    class Config:
        ext

Trigger and perform the auto-completion.

Expected behavior
The plugin adds the import if there is no import so far.
If pydantic is imported in another way already, the plugin adds the appropriate import, like in the examples below

# import is already present
import pydantic


class M(pydantic.BaseModel):
    class Config:
        extra = pydantic.Extra.ignore

# alias import 
import pydantic as p


class M(pydantic.BaseModel):
    class Config:
        extra = p.Extra.ignore

Screenshots

Environments (please complete the following information):

• IDE: PyCharm Professional 2022.1
• OS: macOS 12.3.1
• Pydantic Version: 1.9.0
• Plugin version: 0.3.12

Additional context
Add any other context about the problem here.