Support stop tokens

[s13n]

Since C++20 with std:jthread, there is support for stop tokens in condition variables. It would be nice if the interprocess condition variables would support them, too!

[igaztanaga]

Sadly Interprocess condition variables are optimimally wrappers around OS primitives (like POSIX condition variables), so stop_token support can't be added (e..g std::condition_variable does not support it). But maybe we can analyze if boost::interprocess::condition_variable_any can support it just like std::condition_variable_any.