CMake needs following two changes which were missed part from https://github.com/grpc/grpc/pull/37919 to make CMake use C++17.
- **Explicitly require C++17 for gRPC targets using `cxx_std_17`**: This ensures that gRPC build targets are built with the correct C++17 support.
- **Enforce C++17 for all CMake invocations using `CMAKE_CXX_STANDARD=17`**: This is necessary due to Abseil's API changes depending on the C++ standard used. (e.g. Abseil's `absl::string_view` is implemented differently depending on the C++ standard. Before C++17, it's a distinct type. From C++17 onwards, it's simply an alias for `std::string_view`.) To maintain consistency and avoid build errors, all CMake builds (except particular build tests targetting C++20 or C++23) are now configured to use C++17.
The requirement of C++17 for building gRPC should be documented in the release notes and build instructions.
Closes#38335
PiperOrigin-RevId: 712926964
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
Yash Tibrewal