Configurable per-test shema

[ngan]

Would be cool to be able to configure the schema at the per-test level. Maybe something like:

describe 'foobar', type: :graphql do
  schema FoobarSchema

  it '...' {}
end

describe 'foobar', type: :graphql do
  schema(FoobarSchema) do
    # Annoymous schema, similar to anonymous controllers.
    # Add stuff in this new schema here...
  end

  it '...' {}
end