Implement a tuning plugin for the lee controller

[knmcguire]

We just added the lee controller to work on the crazyflie, but the yaw gains and forward gains aren't great yet. However, Gazebo doesn't allow tuning of the gains unless this has been explicitly 'exposed' in the plugin.

• Create a new gazebo system plugin that is a copy of the multicopter_velocity_controller plugin. The expection is that the controller parameters are non-constant and can take the input of a gz topic (similar way as how the joint position controller does this but then with gains).
• Create a new gazebo gui plugin with sliding bars such that these values can be easily tuned, similar to the slidingbars used here: https://github.com/gazebosim/gz-sim/tree/gz-sim8/src/gui/plugins/joint_position_controller.

Currently this is purely for the purpose of tuning the lee controller, but if it is cleaned up, we might be able to contribute it back to Gazebo itself.

[knmcguire]

Closed because I've made something hacky here: https://github.com/knmcguire/gz-plugin-multicopter-velocity-tuning