Support a configurable GraphQL request timeout for both reactive and synchronous controllers

[tstocker-black-cape]

Now that reactive request cancellation is supported (#1149), it would be really nice if we could configure a request timeout for a server. An example use case for this is a GraphQL server that lives behind a reverse proxy and the reverse proxy has a configured max timeout. In this scenario, a may request a GraphQL request and proxy returns a 408, but the server is still executing the potentially long running work. If the server sets the request timeout to the same value as the reverse proxy, it can avoid spending resources processing requests that have already been terminated.

For Reactive requests, the timeout value should be set. For synchronous/virtual thread calls, thread interrupts could be leveraged.

I'd like to see some simple configuration like spring.graphql.timeout=10s

[bclozel]

Isn't that what #450 is all about?

[tstocker-black-cape]

Ah! Yes it is. For some reason I recall that one being closed, so I was just attempting to re-raise the issue. Sorry for the duplicate!