feat: add websocket support for subscriptions via crossws

[tobiasdiez]

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Wait until h3 "offically" supports it, i.e. there is a stable release with crossws support: https://github.com/unjs/h3/releases

This is a step towards https://github.com/tobiasdiez/nuxt-graphql-server/issues/23.

Afterwards, add a short example to https://github.com/enisdenjo/graphql-ws/blob/master/website/src/pages/recipes.mdx