Require C++17 to match ament_index_cpp 1.8.3+

[marcoag]

This PR tries to fix the current regression in Jazzy by setting CMAKE_CXX_STANDARD 17 to aligning behaviortree_cpp_v3 with ament_index_cpp.

Why:

behaviortree_cpp_v3 is failing to build against ament_index_cpp 1.8.3 because get_package_share_directory.hpp now unconditionally includes <filesystem>, which requires C++17. This package was explicitly setting CMAKE_CXX_STANDARD 14, which caused the compilation to fail when including that header.

The breakage should not be blamed on the ament_index_cpp since the package has required C++17 since version 1.7.0 (commit ament/ament_index@43e7b00, Aug 2023): and Jazzy was released 2024-05-23.

AFAIK there shouldn't be any downstream impact out of this change since behaviortree_cpp_v3 does not export its C++ standard requirement to consumers