[`trac_ik_kinematics_plugin`]: Add support for ROS 2

[aprotyas]

From #1, the primitive directives are:

• Write the plugin for moveit2.
• Update moveit documentation about the trac_ik library and about writing said plugins.

[aprotyas]

I'm labeling this Help Wanted because I have zero experience with MoveIt!, but that's always a learning opportunity...

[130s]

Came from https://bitbucket.org/traclabs/trac_ik/issues/68/ros2-support#comment-60898131

Assuming this repo is a fork from there, why don't you open a PR to that repo? That may accelerate the work to port trac-ik to ros2.