fix: remove hard-coded overwrite_files in AzureStorage

The overwrite_files is True by default, and should be settable from the
django settings using AZURE_OVERWRITE_FILES.

Removing this override will keep the default behaviour (True), while
still allowing users to change it.

NOTE: this change is important because django / django-storages changed
the semantics of the .exists() function, which now returns whether a
path is free for upload (and not whether the file already exists on the
remote storage). With overwrite_files set to True, .exists() will now
always return False.

See jschneier/django-storages#1430

django_storage_url/backends/az.py

@@ -3,6 +3,7 @@
 
 import furl
 from storages.backends import azure_storage
+from django.conf import settings
 
 
 class AzureStorageFile(azure_storage.AzureStorageFile):
@@ -56,7 +57,8 @@ def __init__(self, dsn):
         self.azure_container = container_name
         self.azure_ssl = secure_urls
         self.max_memory_size = 10 * 1024**2
-        self.overwrite_files = True
+        # The default is False in the superclass
+        self.overwrite_files = getattr(settings, "AZURE_OVERWRITE_FILES", True)
         self.location = ""
         self.base_url = str(base_url)