storage manager: add backblaze b2 backend.

app/logical/storage_manager/cloud.rb

@@ -0,0 +1,27 @@
+class StorageManager::Cloud < StorageManager
+  attr_reader :bucket, :client, :fog_options
+
+  def initialize(bucket, client: nil, fog_options: {}, **options)
+    @bucket = bucket
+    @fog_options = fog_options
+    @client = client || Fog::Storage.new(**fog_options)
+    super(**options)
+  end
+
+  def store(io, path)
+    data = io.read
+    client.put_object(bucket, path, data)
+  end
+
+  def delete(path)
+    client.delete_object(bucket, path)
+  end
+
+  def open(path)
+    file = Tempfile.new(binmode: true)
+    response = client.get_object(bucket, path)
+    file.write(response.body)
+    file.rewind
+    file
+  end
+end