new fields added to Snapshot

interface/storage/Snapshot.py

+import json
+
+
 class Snapshot:
-    def __init__(self, id, size) -> None:
+    def __init__(self,
+                 id,
+                 volume_id,
+                 size,
+                 status,
+                 created_at
+                 ) -> None:
         super().__init__()
 
         self.id = id
+        self.volume_id = volume_id
         self.size = size
+        self.status = status
+        self.created_at = created_at
+
+    def __str__(self) -> str:
+        return self.toJSON()
+
+    def toJSON(self):
+        return json.dumps(self.__dict__)