Issue warning if pixhawk is only powered of servo rail

I had not realized there was a failure with the wires going to the Power input on the pixhawk and Mission Planner did not submit a warning for this in any way. The information was there under the parameter "voltageflag" and it stated "Servo_/" which I am assuming means it is powering the pixhawk off of the servo rail, but, it is very difficult to find this or even know what it means. There is no description for this flag anywhere and no warning is given.

Could we add a warning like all other flags if servo rail is powering the pixhawk, at least for APM Plane where servo rail voltage can be quite unstable if servos are working hard?

When extracting the .csv file the "Flag" only reports as the number 2. Again, there is no explanation of what this means.

Start in Mission Planner by locating where the "voltageflag" parameter is interpreted and where the CSV export produces the numeric "Flag" value. Check the APM Plane handling first, then trace the existing warning flags. Done means a clear warning appears when the Pixhawk is powered from the servo rail and the exported value is explained rather than shown only as 2.

Written by the indexing model from the issue text.