Public Changes -
* Add a pkgconfig installer for `grpcpp_otel_plugin`
Example Changes -
* Add example of how to use the pkgconfig for `grpcpp_otel_plugin` with the existing OpenTelemetry example.
* Add another OpenTelemetry example that uses OTel's OStream exporter. This makes it easier to test the pkgconfig file for `grpcpp_otel_plugin` since the OStream exporter does not require any additional dependencies, as opposed to the Prometheus exporter.
Test changes -
* Modify `run_distrib_test_cmake_pkgconfig.sh` test to install opentelemetry and build the example with the OStream exporter.
Closes#36686
PiperOrigin-RevId: 636965475
Changes -
* Add CMake build support to `grpcpp_otel_plugin`. Currently, we are only supporting the `find_package CONFIG` method for depending on `opentelemetry-cpp`.
* Since, `grpcpp_otel_plugin` is an extension of gRPC, it will not be built by default. To enable building of this target, a new CMake option `gRPC_BUILD_GRPCPP_OTEL_PLUGIN` is being added.
* Also add `CMakeLists.txt` to the otel example.
The `otel_plugin_test` can also be built through cmake but, for the CI to work, there are some additional changes. Those will be made in an upcoming PR.
Closes#36063
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36063 from yashykt:OTelCMakeSupport 3bc783823b17ed282ae9b6b7bf8a26cedaae30f9
PiperOrigin-RevId: 613734473
