Add option to limit convoy travel distances.

CPU load seems to scale with route length, so add an option to limit
the length of the convoy route. The tradeoff is that the performance
sensitive route won't necessarily be a correct route.

game/settings/settings.py

@@ -407,6 +407,12 @@ class Settings:
         section=PERFORMANCE_SECTION,
         default=True,
     )
+    convoys_travel_full_distance: bool = boolean_option(
+        "Convoys drive the full distance between control points",
+        page=MISSION_GENERATOR_PAGE,
+        section=PERFORMANCE_SECTION,
+        default=True,
+    )
     perf_infantry: bool = boolean_option(
         "Generate infantry squads alongside vehicles",
         page=MISSION_GENERATOR_PAGE,