HUD: add ESC health label

Similar to our EKF and Vibration status reporting, I think we should add an ESC health reporting label and pop-up window. The label should probably be white most of the time but turn red if the ESCs start reporting errors. @peterbarker says that the [SYS_STATUS message](https://mavlink.io/en/messages/common.html#SYS_STATUS) already includes a MAV_SYS_STATUS_SENSOR_MOTOR_OUTPUTS bit that AP sets if the ESCs start producing errors.

Perhaps the label should only appear if the ground station is receiving [ESC_TELEMETRY messages](https://mavlink.io/en/messages/ardupilotmega.html#ESC_TELEMETRY_1_TO_4).

If the user clicks on this label we should probably display the RPM, Temperature and error count for the ESCs

This comes in response to [this 4.6 user crash](https://discuss.ardupilot.org/t/copter-flipped-and-crashed-ekf3-innovations-high-seeking-help-for-analysis/134912/7) in which the ESCs started reporting errors a full 4 minutes before the vehicle actually crashed.

Start with the HUD's existing EKF and Vibration status reporting, then trace how SYS_STATUS and ESC_TELEMETRY messages are handled. Done means an ESC health label appears when ESC telemetry is received, changes to red on reported errors, and opens a view showing RPM, temperature, and error counts.

Written by the indexing model from the issue text.