Add a real CAS ingress point.

Putting the ingress point directly on one end of the FLOT means that AI
flights won't start searching and engaging targets until they reach that
point. If the front line has advanced toward the flight's departure
airfield, it might overfly targets on its way to the IP.

Instead, place an IP for CAS the same way we place any other IP. The AI
will fly to that and start searching from there.

This also:

* Removes the midpoint waypoint, since it didn't serve any real purpose
* Names the FLOT boundary waypoints for what they actually are

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/2231.

game/persistence/paths.py

@@ -29,3 +29,7 @@ def save_dir() -> Path:
 
 def mission_path_for(name: str) -> Path:
     return Path(base_path()) / "Missions" / name
+
+
+def waypoint_debug_directory() -> Path:
+    return liberation_user_dir() / "Debug/Waypoints"