Passing additional context to updaters

[ethanjweiner]

Hello,

I have the following use case: I update Entity A via a mutation executor, and need to invalidate certain keys on unrelated Entity B. I need to pass an identifier for Entity B to the mutation context to be able to invalidate it from an updater.

I've tried passing an additional variable to the mutation (supported since this PR), but most GraphQL server implementations will reject an additional variable if it's not used actually used by the underlying operation. It also doesn't appear that updaters can access custom OperationContext passed to executeMutation.

Am I missing something obvious here?