Rework grpc cancelation propagation

[laurit]

Resolves #8923
When running with the agent we switch grpc context storage to use opentelemetry context. As described in #4169 (comment) this strategy works too well, context propagation sometimes happens when originally context was not propagated. This has the side effect of also propagating deadlines to calls that previously didn't have them. This is corrected in #5543 Unfortunately this has the side effect that now deadlines and cancellations aren't sometimes propagated when they are with the original context store implementation. #8924 introduces a flag that allows users to decide whether cancelation and deadlines should propagate. Such flags aren't ideal because users need to figure out what works for them. This pr explores an alternative strategy where, instead of completely replacing the original context storage, we'll track propagation through both otel context and the original context storage. When we discover that context was propagated through otel, but not with the original context storage, we'll fork the grpc context to break cancellation propagation. Hopefully this way deadlines and cancellation are propagated only when they are propagated without the agent. This pr can coexist with the flag introduced in #8924

[mateuszrzeszutek]

@dkharlan Can you take a look at this PR as well?

[dkharlan]

I like it! This is definitely better than mine (#8924), since this implies less knowledge of the problem. I haven't had time to review in detail yet, but I'll try to find some time today or tomorrow to test with our app and report whether it fixes the problem we've observed.

[dkharlan]

Sorry for the delay -- I built the agent from this branch and confirmed that it fixes #8923 for our app. Thanks for jumping on this so quickly!