[Testing utilities] Example with MSW

[alessbell]

Issue Description

Build an example of using proxiedSchema with Mock Service Worker using react-apollo-error-template.

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@apollo/client version

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[alessbell]

@jerelmiller and I had an interesting discovery related to some MSW tests yesterday in which several tests are sharing a client instance: the SuspenseCache was causing tests running serially using the same query in subsequent tests to do an initial render with the old data from the resolvers set in the previous test.

This is due to a setTimeout in the dispose function to work around an issue with strict mode. Jerel had an idea about how we may be able to remove the setTimeout since some of the logic around unsubscribing/resubscribing changed with the introduction of createQueryPreloader.