Introduce C++20 target to avoid usage of deprecated constructs

[elfenpiff]

Brief feature description

Some constructs like std::result_of where deprecated in C++17 and are no longer supported with C++20. A c++20 CI target would help avoiding such constructs right from the beginning so that iceoryx can be used also in C++20 projects.

At the moment GTest 1.10 is not working with C++20. Either we use a more modern version or skip unit tests on that target for the time being. This should be alright since we are aiming to use iceoryx in C++20 projects as a library. So the test should not be required.