Let the TheaterCommander manage front line stance.

This improves the AI behavior by choosing the stances non-randomly:

* Breakthrough will be used if the base is expected to be capturable and
  the coalition outnumbers the enemy by 20%.
* Elimination will be used if the coalition has at least as many units
  as the enemy.
* Defensive will be used if the coalition has at least half as many
  units as the enemy.
* Retreat will be used if the coalition is significantly outnumbers.

This also exposes the option to the player.

game/commander/garrisons.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 from collections import Iterator
 from dataclasses import dataclass
 
-from game.theater import ConflictTheater
+from game.theater import ConflictTheater, ControlPoint
 from game.theater.theatergroundobject import VehicleGroupGroundObject
 from game.utils import meters, nautical_miles
 
@@ -53,9 +53,7 @@ class Garrisons:
                 continue
 
             for garrison in garrisons:
-                # Not sure what distance DCS uses, but assuming it's about 2NM since
-                # that's roughly the distance of the circle on the map.
-                if meters(garrison.distance_to(cp)) < nautical_miles(2):
+                if meters(garrison.distance_to(cp)) < ControlPoint.CAPTURE_DISTANCE:
                     blocking.append(garrison)
                 else:
                     defending.append(garrison)