Add jalali date formatting utility and update invoice generation

backend/utils/jalali_formatter.py

@@ -0,0 +1,17 @@
+import jdatetime
+from django.utils import timezone
+
+def to_jalali(dt):
+    if not dt:
+        return None
+
+    dt = timezone.localtime(dt)
+
+    return jdatetime.datetime.fromgregorian(
+        year=dt.year,
+        month=dt.month,
+        day=dt.day,
+        hour=dt.hour,
+        minute=dt.minute,
+        second=dt.second,
+    )