Add campaign support for ferry-only bases.

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/3170.

tests/campaignloader/test_controlpointconfig.py

@@ -0,0 +1,30 @@
+from game.campaignloader.controlpointconfig import ControlPointConfig
+
+
+def test_from_empty_data() -> None:
+    config = ControlPointConfig.from_data({})
+    assert not config.ferry_only
+
+
+def test_from_data() -> None:
+    config = ControlPointConfig.from_data(
+        {
+            "ferry_only": True,
+        }
+    )
+    assert config.ferry_only
+
+
+def iter_from_data() -> None:
+    data = dict(
+        ControlPointConfig.iter_from_data(
+            {
+                0: {},
+                "named": {"ferry_only": True},
+            }
+        )
+    )
+    assert data == {
+        0: ControlPointConfig(ferry_only=False),
+        "named": ControlPointConfig(ferry_only=True),
+    }