Add basic backend infrastructure

Signed-off-by: Felipe Cardoso <felipe.cardoso@hotmail.it>

backend/app/models/sample.py

@@ -0,0 +1,11 @@
+from datetime import datetime
+from typing import Optional
+
+from pydantic import BaseModel
+
+
+class Sample(BaseModel):
+    filename: str
+    url: str
+    created_at: datetime
+    step: Optional[int] = None