Add support for DCS 2.9's AI unlimited fuel.

This is enabled by default because I can't think of a time where it's
ever been more fun to watch the AI run out of fuel after cycling between
afterburner and speedbrake for twenty minutes.

This is only lightly tested (I verified that the task shows up
appropriately in the ME when set, not when unset, and never for
players), since the interesting part of the implementation is up to ED.

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/3201.

game/settings/settings.py

@@ -339,6 +339,18 @@ class Settings:
     )
 
     # Gameplay
+    ai_has_unlimited_fuel: bool = boolean_option(
+        "Unlimited fuel for AI flights",
+        page=MISSION_GENERATOR_PAGE,
+        section=GAMEPLAY_SECTION,
+        default=True,
+        detail=(
+            "If enabled, AI-only flights will have unlimited fuel. This can be "
+            "disabled to force AI flights to play by the same rules as players, but be "
+            "warned that the DCS AI is not particularly fuel conscious, so will often "
+            "run out of fuel when players would not."
+        ),
+    )
     fast_forward_to_first_contact: bool = boolean_option(
         "Fast forward mission to first contact (WIP)",
         page=MISSION_GENERATOR_PAGE,