Add sentry-trace header about apollo-link-sentry HOT 4 CLOSED

https://docs.sentry.io/platforms/javascript/guides/react/performance/instrumentation/automatic-instrumentation does this. We had to make sure that the Sentry setup is imported before the Apollo setup though, due to getsentry/sentry-javascript#2860 (comment)

// The side effect of patching fetch() has to occur before configuring Apollo Client
// https://github.com/getsentry/sentry-javascript/issues/2860#issuecomment-684514367
import './sentry';
import { ApolloProvider } from '@apollo/client';

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@spawnia sorry following up on this cause I noticed the instructions suggest adding:

    new Sentry.BrowserTracing({ traceFetch: false }),

which would disable the sentry-trace header.

from apollo-link-sentry.

I guess it's not obvious in the README section if 1 and 2 are alternatives or both are needed

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But if the README says we should disable the fetch instrumentation for GraphQL, then we still don't get a trace ID, right, @spawnia?

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