Add setting to increase cost/distance of aircraft linkgraph links

src/lang/english.txt

@@ -2309,6 +2309,9 @@ STR_CONFIG_SETTING_DEMAND_SIZE_HELPTEXT                         :Setting this to
 STR_CONFIG_SETTING_SHORT_PATH_SATURATION                        :Saturation of short paths before using high-capacity paths: {STRING2}
 STR_CONFIG_SETTING_SHORT_PATH_SATURATION_HELPTEXT               :Frequently there are multiple paths between two given stations. Cargodist will saturate the shortest path first, then use the second shortest path until that is saturated and so on. Saturation is determined by an estimation of capacity and planned usage. Once it has saturated all paths, if there is still demand left, it will overload all paths, prefering the ones with high capacity. Most of the time the algorithm will not estimate the capacity accurately, though. This setting allows you to specify up to which percentage a shorter path must be saturated in the first pass before choosing the next longer one. Set it to less than 100% to avoid overcrowded stations in case of overestimated capacity.
 
+STR_CONFIG_SETTING_AIRCRAFT_PATH_COST                           :Scale distance of paths which use aircraft: {STRING2}
+STR_CONFIG_SETTING_AIRCRAFT_PATH_COST_HELPTEXT                  :This scales the cost (distance metric) of paths which use aircraft, such that they appear longer/less direct than they actually are. The reduces the tendency for direct routes using aircraft to become heavily overloaded.
+
 STR_CONFIG_SETTING_LOCALISATION_UNITS_VELOCITY                  :Speed units: {STRING2}
 STR_CONFIG_SETTING_LOCALISATION_UNITS_VELOCITY_HELPTEXT         :Whenever a speed is shown in the user interface, show it in the selected units
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