Throttle limit feature (#5608)

Adds new throttle_limit_type and throttle_limit_percent parameters that allow the pilot to limit the maximum commanded throttle seen by the flight controller by either scaling or clipping the maximum throttle.  The default is 100 representing no limiting.  So as an example, if a pilot was to set throttle_limit_type = SCALE and throttle_limit_percent = 80 the throttle input would scale from 0 to 80% based on full stick deflection from the radio.

This capability replaces the method of limiting throttle in the radio which some pilots are using to manage throttle on tight courses or reduce overall battery consumption when the extra power isn't needed.

There is no effect on the maximum throttle seen by the motors so the mixer still has full authority.

src/main/interface/settings.h

@@ -87,6 +87,7 @@ typedef enum {
 #ifdef USE_DUAL_GYRO
     TABLE_GYRO,
 #endif
+    TABLE_THROTTLE_LIMIT_TYPE,
     LOOKUP_TABLE_COUNT
 } lookupTableIndex_e;