docs: new path for useServer v6 and up

[jchanke]

useServer should be imported from the path graphql-ws/use/ws instead of graphql-ws/lib/use/ws, starting from graphql versions 6.0.0 and up.

see enisdenjo/graphql-ws#617

[apollo-cla]

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[glasser]

Hi, are you sure that's the only change? In addition to another import in the same file, the code shows a few calls to useServer with methods whose options may have changed.

I can try to make the other changes myself but as I don't really actively use this WS support, it's easier to validate when the PR comes from somebody successfully using graphql-ws. Are you able to audit the calls to useServer in the file and update them too?

(We really only have this doc page as a replacement for the fact that we had subscriptions built in way back in Apollo Server v2; at some point we should just delete it and simply have a sentence somewhere noting that graphql-ws exists and is well-documented...)

[jchanke]

Thanks for pointing that out. I'll look into that as well!