Add the ability to specify `GraphQLResolveInfo.context` type

[fedirz]

Currently, GraphQLResolveInfo.context is being typed as Any, making GraphQLResolveInfo a generic would give users the ability to provide their type. This is already being done in GraphQL.js

export type GraphQLFieldResolver<
  TSource,
  TContext,
  TArgs = any,
  TResult = unknown,
> = (
  source: TSource,
  args: TArgs,
  context: TContext,
  info: GraphQLResolveInfo,
) => TResult;

If this change will be welcome, I'd like to make a pull-request implementing it.

[Cito]

Sure, PRs of that kind are always welcome.