Added warning if in docker and data dir isn't mounted

Had to remove the VOLUME definition in the dockerfile for this, otherwise the data dir would always be mounted by an anonymous volume if the user didn't mount it correctly, so the python script wouldn't be able to detect it.

spoolman/env.py

@@ -326,3 +326,16 @@ def check_write_permissions() -> None:
                 gid,
             )
             sys.exit(1)
+
+
+def is_docker() -> bool:
+    """Check if we are running in a docker container."""
+    return Path("/.dockerenv").exists()
+
+
+def is_data_dir_mounted() -> bool:
+    """Check if the data directory is mounted as a shfs."""
+    # "mount" will give us a list of all mounted filesystems
+    mounts = subprocess.run("mount", check=True, stdout=subprocess.PIPE, text=True)  # noqa: S603, S607
+    data_dir = str(get_data_dir().resolve())
+    return any(data_dir in line for line in mounts.stdout.splitlines())