feat: enable withFilter ResolverFn to return Promise

[janhalama]

Use case: asyncIteratorFn of withFilter is place where I want to authorize subscription, authorization should not be implemented in GraphQL resolvers, I want to delegate authorization logic to the business layer which is in our case implemented in another service, that is why I need to change result of ResolverFn to Promise<AsyncIterator> to be able to await for the result of the service call in asyncIteratorFn handler

[emaciel10]

Any reason why this one hasn't been merged in? We feel like it would be really useful for our workflow as well!

[grantwwu]

Isn't this a breaking change?

[simonsterckx]

Would like to have this functionality too! We could just check if the return value is a promise before resolving it to ensure backward compatibility.

[janhalama]

@simonsterckx @grantwwu thanx for your comments, please see my latest update to this PR, I moved required functionality into new function withFilterAsync, withFilter function remains unchanged.

[emaciel10]

@simonsterckx @grantwwu bump! Anything I can do to keep this PR moving? It would be great if we could get this functionality merged in

[grantwwu]

Hey, until I see more activity from Apollo with regards to helping me do code reviews and participating in the maintenance of this - there doesn't seem to have been a post in the #contributing channel of the Apollo Spectrum chat for several months now - I'm going to put my participation on hold here, for two reasons:

• Even though I can merge stuff in, I can't release it on NPM. So there's no point in my merging it.
• I recently left my job which uses GraphQL subscriptions. I'm going to be joining a company in November which most likely does not.

[hwillson]

It sounds like this was addressed in #220 (which is coming in 3.0). Let us know if not - thanks for this contribution (and sorry for the delay!).