This PR aims to de-experimentalize the APIs for GCP Observability.
We would have ideally wanted public feedback before declaring the APIs
stable, but we need stable APIs for GA.
Changes made after API review with @markdroth @veblush, @ctiller and the
entire Core/C++ team -
* The old experimental APIs `grpc::experimental::GcpObservabilityInit`
and `grpc::experimental::GcpObservabilityClose` are now deprecated and
will be deleted after v.1.55 release.
* The new API gets rid of the Close method and follows the RAII idiom
with a single `grpc::GcpObservability::Init()` call that returns an
`GcpObservability` object, the lifetime of which controls when
observability data is flushed.
* The `GcpObservability` class could in the future add more methods. For
example, a debug method that shows the current configuration.
* Document that GcpObservability initialization and flushing (on
`GcpObservability` destruction) are blocking calls.
* Document that gRPC is still usable if GcpObservability initialization
failed. (Added a test to prove the same).
* Since we don't have a good way to flush stats and tracing with
OpenCensus, the examples required users to sleep for 25 seconds. This
sleep is now part of `GcpObservability` destruction.
Additional Implementation details -
* `GcpObservability::Init` is now marked with `GRPC_MUST_USE_RESULT` to
make sure that the results are used. We ideally want users to store it,
but this is better than nothing.
* Added a note on GCP Observability lifetime guarantees.
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Yash Tibrewal