feat(multi-tenant): define the send status and bounce type

apps/notification/common/constants/email.py

@@ -0,0 +1,15 @@
+from enum import Enum
+
+class EmailSendStatus(Enum):
+    PENDING = "pending"
+    SENDING = "sending"
+    SENT = "sent"
+    FAILED = "failed"
+    BOUNCED = "bounced"
+
+class BounceType(Enum):
+    HARD_BOUNCE = "hard_bounce"
+    SOFT_BOUNCE = "soft_bounce"
+    SPAM_REPORT = "spam_report"
+    UNSUBSCRIBE = "unsubscribe"
+    BLOCKED = "blocked"