Made enums.py for all the enums to avoid cyclic imports.

Signed-off-by: Cliff Hill <Clifford.hill@gsa.gov>

app/billing/billing_schemas.py

@@ -1,5 +1,7 @@
 from datetime import datetime
 
+from app.enums import NotificationType
+
 create_or_update_free_sms_fragment_limit_schema = {
     "$schema": "http://json-schema.org/draft-07/schema#",
     "description": "POST annual billing schema",