ROS2 code generation for OCP solvers

[alphaville]

Currently, ROS nodes support the following messages

float64[]      parameter         # parameter p (mandatory)
float64[]      initial_guess     # u0 (optional/recommended)
float64[]      initial_y         # y0 (optional)
float64        initial_penalty   # initial penalty (optional)

which means that the called needs to specify the parameter, e.g.,

ros2 topic pub --once /{{ros.subscriber_subtopic}} \
  {{ros.package_name}}/msg/OptimizationParameters \
  "{parameter: [YOUR_PARAMETER_VECTOR], \
    initial_guess: [INITIAL_GUESS_OPTIONAL], \
    initial_y: [], initial_penalty: 15.0}"

It will be a lot more convenient if the parameters are replaced by OCP-type parameters (e.g., x0), when the solver is generated using the ocp module.