Supervisor container startup health function (#2214)

* Supervisor container startup health function

* better struct

* add test

* address comment

* rename file

* Update tests/test_main.py

Co-authored-by: Stefan Agner <stefan@agner.ch>

Co-authored-by: Stefan Agner <stefan@agner.ch>

tests/test_main.py

@@ -0,0 +1,17 @@
+"""Testing handling with main."""
+from pathlib import Path
+
+import supervisor.__main__ as main
+
+
+def test_write_state(tmp_path):
+    """Test startup-marker file cleanup."""
+    test_file = Path(tmp_path, "test.file")
+
+    test_file.touch()
+    assert test_file.exists()
+
+    main.CONTAINER_OS_STARTUP_CHECK = test_file
+    main.run_os_startup_check_cleanup()
+
+    assert not test_file.exists()