fix: Fixed race condition in action server between is_ready and take" (…

…ros2#2495)

Some background information: is_ready, take_data and execute data
may be called from different threads in any order. The code in the old
state expected them to be called in series, without interruption.
This lead to multiple race conditions, as the state of the pimpl objects
was altered by the three functions in a non thread safe way.

Co-authored-by: William Woodall <william@osrfoundation.org>
Signed-off-by: Janosch Machowinski <J.Machowinski@cellumation.com>