[IJ Plugin] Warn when .graphqlrc files are present

[BoD]

When using a v4 project, the location of the schema and operation files is automatically contributed to the GraphQL IJ Plugin by the Apollo plugin. Therefore .graphqlrc (and variants like graphql.config.yml, etc.) aren't necessary anymore, and in fact having them in the project is probably confusing.

A warning explaining this, with a quick fix to delete the files could be implemented.

This could also be part of the migration 3.x -> 4.x