LSP: warn on `fields="__all__"` and add code action to expose all fields

[patrick91]

We don't have an LSP for Strawberry Django, but in case we add one I think this feature would be neat to have.

We allow to use fields="__all__", which might lead to security issues, so the LSP could warn when using that, and also provide a code action that does what __all__ does, but with code

From this:

@strawberry.django.type(models.Flyer, fields="__all__")
class Flyer:
    ...

To this:

@strawberry.django.type(models.Flyer)
class Flyer:
    id: auto
    title: auto

We could also add code action to expose additional fields :)