Provide a public experimental API and bazel compatible build target for OpenTelemetry metrics.
Details -
* New `OpenTelemetryPluginBuilder` class that provides the API specified in https://github.com/grpc/proposal/blob/master/A66-otel-stats.md
* The existing `grpc::internal::OpenTelemetryPluginBuilder` class is moved to `grpc::internal::OpenTelemetryPluginBuilderImpl` for disambiguation.
* Renamed `OTel` in some instances to `OpenTelemetry` for consistency.
Closes#35348
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35348 from yashykt:OTelPublicApi e32328825e
PiperOrigin-RevId: 594271246
Earlier, the grpc message-length prefix for outgoing data messages was
incorrectly being counted towards `data_bytes` instead of
`framing_bytes`. This PR fixes it.
Note that the incoming stats collection properly attributes the grpc
message-length prefix to `framing_bytes`.
This change will affect all stats plugins (OpenCensus and OpenTelemetry)
that make use of this information for metrics.
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@ctiller PTAL for core configuration changes. I converted the type from
std::function to absl::AnyInvocable. Do you think the functor in
RegisteredBuilder should be callable just once or multiple times?
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A new metadata type `x-envoy-peer-metadata` is being introduced. We
don't have a better way to do this at the moment compared to just adding
it in `metadata_batch.h`.
The GSM Observability plugin uses this metadata to send topology
information to peers in the form of serialized and base64 encoded
`google::protobuf::Struct`. The individual keys being used inside the
struct are subject to change.
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Based on updates at https://github.com/grpc/proposal/pull/380
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Based on updates at https://github.com/grpc/proposal/pull/380
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Note that the plugin is still under `grpc::internal` namespace and not
under `experimental` intentionally.
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