I've added a queue depth of 4 for sensor_accel and sensor_gyro. This is initially added because it's not always possible for the `vehicle_acceleration` to keep up with every publication of the primary accelerator as it runs in the same thread as ekf2, various controllers, etc.
Later this mechanism will be used in a few areas
- rate limit `vehicle_angular_velocity` and `vehicle_acceleration` without missing any raw data
- move IMU integration to `vehicle_imu` and out of the actual driver threads, eliminating the need for sensor_accel_integrated and sensor_gyro_integrated
- integrate raw gyro synchronized with optical flow measurements
* adds a work_queue systemcmd that will bring a tree view of all active work queues and work items
* WorkQueues now track attached WorkItems and will shutdown when the last WorkItem is detached
rfu