AP_Stats: Make cumulative flight time updates optional

[muramura]

Flight time for unmanned aircraft in Japan is defined as the time from the first takeoff until the power is turned off.
ArduPilot defines flight time as the time from takeoff to landing.
I would like to add the option to use the flight time in the country of Japan as the cumulative flight time.

AND

Update time is optional.
This is because a 30 second update is very long when displaying accumulated flight time.

This is part of the flight record established by the Japanese Civil Aviation Bureau.
(1) Flight record
(a) Flight records shall be recorded for each flight.
(b) One flight in the flight log shall be defined as the time when the unmanned aircraft takes off from the place of departure after activating the power supply, lands at the destination, and then deactivates the power supply. For example, if, after landing at the destination, the power is turned off to load or unload luggage, change batteries, etc., the flight is considered to be one, but if the aircraft departs for another point with the power activated, or if it continuously takes off and lands, the flight is considered to be one until it lands at the final destination and the power is turned off. If, after landing at the final destination, the aircraft makes a landing including a continuous takeoff and landing at another point before turning off the power supply, this point shall be entered in the flight record as a transit point. However, under operational conditions In such cases, however, the flight record shall include the actual flight time. In such cases, efforts should be made to grasp and manage the actual flight time.