adds target-exchange and initial migrations

api/exceptions.py

@@ -14,8 +14,8 @@ class ApiException(Exception):
         return rv
 
 class NotFoundException(ApiException):
-    def __init__(self, message) -> None:
-        super().__init__(404, message)
+    def __init__(self, entity_name) -> None:
+        super().__init__(404, f'{entity_name} could not be found')
 
 class BadRequestException(ApiException):
     def __init__(self, message) -> None: