Add missing schema args to applyGraphQL

[justinmchase]

Here: https://github.com/aaronwlee/oak-graphql/blob/0.6.2/applyGraphQL.ts#L29-L39

I am already making my own schema by calling makeExecutableSchema which includes schemaTransforms: []...

It would be great if you could add schemaTransforms: [] args and pass that into the call to makeExecutableSchema and/or support a schema: GraphQLSchema arg which would be mutually exclusive with the other three args and would skip the call to makeExecutableSchema.

Something like that, as it is I can't quite use it.

I was going to pull it in to get the websocket stuff but I see that's not quite ready too. I'll probably switch to this lib after these.