Subscription redundant wrapper

See here https://github.com/apollographql/graphql-testing-library/blob/05fed23d8414abef1cb00f70ec2cbee121f477c6/demo/server/src/index.ts#L191

This should be `pubsub.publish("NUMBER_INCREMENTED", currentNumber)` instead. The wrapper object contains the subscription name.

Also it would be good to have some sort of lightweight pubsub for testing. https://github.com/apollographql/graphql-subscriptions is too much for me and actually unusable because there's no built-in browser api, it uses node's `events` package which I don't have in the browser tests. I do happen to have rxjs, so I'm using that, I did have to pull in some async iterator converter though. And I also don't need the event name, I just want to publish the same type of event for this particular subscription.

Maybe rethink the api for subscription? Not even sure what the "resolve" method is for and having the underlying "subscribe" is unintuitive. Maybe just accept what subscribe accepts or just the pubsub api you come up with

Start at demo/server/src/index.ts around line 191 and inspect how the subscription wrapper and underlying subscribe/resolve API are used. Define a browser-compatible lightweight pubsub approach and clarify the subscription API, with completion requiring direct event payloads and behavior that works in the browser testing setup.

Written by the indexing model from the issue text.