Allow to rename thread in RealtimePublisher

[roncapat]

At least in Linux, it is possible to rename a thread, via calls like ptrhead_setname_np.

For application featuring many RealtimePublishers and many other threads, diving into perf record outputs (e.g. via hotspot tool) is difficult because by default all threads have the same name (First 15 characters of the process name), and thread renaming is a powerful tool to discriminate at a glance which thread does what.

To allow this, either the implementation of RealtimePublisher shall permit to obtain the native handle (see this) or may enable for Linux only an additional method that uses pthread_setname_np.

I can submit a PR depending on maintainers feedback of course 👍🏻

[christophfroehlich]

@saikishor what do you think?