app/main.py: Fix default storage_path (#7)

Previously, trying to run the container using
the tutorial from the `README.md` led to an error,
due to a wrongly set default storage path if
the environment variable `STORAGE_PATH` is not 
set. This fixes this issue by setting the default
storage path to `/storage` rather than the prior
relative path: `storage`.

server/app/main.py

@@ -8,7 +8,7 @@
 from basyx.aas.backend.local_file import LocalFileObjectStore
 from basyx.aas.adapter.http import WSGIApp
 
-storage_path = os.getenv("STORAGE_PATH", "storage")
+storage_path = os.getenv("STORAGE_PATH", "/storage")
 storage_type = os.getenv("STORAGE_TYPE", "LOCAL_FILE_READ_ONLY")
 base_path = os.getenv("API_BASE_PATH")