Add a flag to `SentryApolloInterceptor` to stop attaching tracing headers for Apollo v2

### Description

There's no URL available before the request goes out in our Apollo v2 integration. We're attaching tracing headers without checking against `tracePropagationTargets`.

We could:
- add an opt-out flag to disable this (recommended)
- remove trace headers from Apollo v2

Start at SentryApolloInterceptor and inspect the Apollo v2 request path, especially how tracing headers are attached without a URL. Confirm the intended opt-out behavior from the issue description, then add coverage for the flag and verify that the headers are absent when it is enabled; done means Apollo v2 supports the documented opt-out without affecting other behavior.

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