Plan move to C++17

According to the Abseil doc:

• https://github.com/abseil/abseil-cpp?tab=readme-ov-file#support

support for C++14 will be revisited on 2024-12-15:

• https://github.com/google/oss-policies-info/blob/main/foundational-cxx-support-matrix.md

Per policies:

• https://opensource.google/documentation/policies/cplusplus-support

C++ 14 will be dropped for C++17:

We will drop support for our oldest supported C++ standard when one of the following happens:

    All supported compilers* default to a newer version
    When 10 years pass since the standard's release date
    Example: In 2023, if all supported compilers use C++17 as their default, then we can drop support for C++14. Otherwise, we'll need to wait until 2024, which would be 10 years after C++14 was released.

When abseil no longer supports C++14 and requires C++17, so will gtest, gmock, grpc, overall forcing opentelemetry-cpp to drop C++14 as well.

We need to plan for this