Allow passing rules directly into the graphql function

I wanted to add some custom validation rules in addition to the default `graphql.specified_rules`. Unless I'm mistaken, the only way to do so is to manually call `validate` with the new rules, which means that I basically have to duplicate all the code inside of `async def graphql`, and change the validation step in order to pass in my custom rules. Is it possible instead to just allow clients to pass the rules they want to use into the top-level `graphql` call?