Feat/kinematics node

[oguzhanbzglu]

Summary

Adds a new kinematics_nodes package that exposes a MoveIt-compatible
GetPositionIK ROS 2 service backed by any kinematics_interface plugin.

Changes

• New package kinematics_nodes with:
  • IKPluginKinematicsServiceNode: loads a KinematicsInterface plugin via pluginlib
    and serves moveit_msgs/srv/GetPositionIK requests
  • Reads robot description from parameter, extracts kinematic chain from URDF
  • Supports optional seed state from the request; falls back to zero if not provided
  • Uses tf2 to resolve flange-to-end-effector transform
  • Returns MoveIt error codes on failure

Depends on

• Const changes in base interface — the current PR uses convert_cartesian_pose_to_closest_joint_state method. Please review that first.