Add a struct for Interface information, update the test URDF

[AndyZe]

Closes #132

[destogl]

Thanks for the effort!

I hope I gave you some good suggestions how to continue. By applying a few suggestions everything will get simpler :)

[destogl]

Looking good. Just a few small corrections.

Thanks for language and grammar corrections 👍

[destogl]

Suggested change

	joint_info_.parameters["max_position"] = "3.14";
	joint_info_.parameters["min_position"] = "-3.14";
	joint_info_.parameters["max"] = "3.14";
	joint_info_.parameters["min"] = "-3.14";

[AndyZe]

See next comment, below

[destogl]

We should also change those into "min" and "max"

[AndyZe]

If I understand correctly, the key of joints[0].parameters can be any string. I believe you are thinking of joints[0].command_interfaces[0].min and joints[0].command_interfaces[0].max

For example, this is perfectly valid:

EXPECT_EQ(hardware_info.joints[0].parameters.at("serial_number"), "A12345C63");

[AndyZe]

A lot of the example URDF has this:

    <joint name="joint1">
      <classType>ros2_control_components/PositionJoint</classType>
      <param name="min_position_value">-1</param>
      <param name="max_position_value">1</param>
    </joint>

Maybe these examples are deprecated and they need to be deleted? Hopefully in a follow-up PR?

[destogl]

Ok, than leave it as it is.

[destogl]

Let us see than later, what we do.

Probably this Example URDFs should go into test_robot_hatdware package.

[destogl]

I am happy now :)

[bmagyar]

Another round of parser update coming shortly, let's merge this in the mean time. Thanks @AndyZe for this work, we'll sort out the min_position_value situation in a follow-up PR.