Add campaign support for ferry-only bases.

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

game/campaignloader/controlpointconfig.py

@@ -0,0 +1,21 @@
+from __future__ import annotations
+
+from collections.abc import Iterator
+from dataclasses import dataclass
+from typing import Any
+
+
+@dataclass(frozen=True)
+class ControlPointConfig:
+    ferry_only: bool
+
+    @staticmethod
+    def from_data(data: dict[str, Any]) -> ControlPointConfig:
+        return ControlPointConfig(ferry_only=data.get("ferry_only", False))
+
+    @staticmethod
+    def iter_from_data(
+        data: dict[str | int, Any]
+    ) -> Iterator[tuple[str | int, ControlPointConfig]]:
+        for name_or_id, cp_data in data.items():
+            yield name_or_id, ControlPointConfig.from_data(cp_data)