fix: schema error codes need to be JSON serializable

[EC-680]

src/schema_registry/routers/errors.py

@@ -3,13 +3,13 @@
 See LICENSE for details
 """
 
-from enum import Enum, unique
+from enum import IntEnum, StrEnum, unique
 from fastapi import HTTPException, status
 from fastapi.exceptions import RequestValidationError
 
 
 @unique
-class SchemaErrorCodes(Enum):
+class SchemaErrorCodes(IntEnum):
     HTTP_BAD_REQUEST = status.HTTP_400_BAD_REQUEST
     HTTP_NOT_FOUND = status.HTTP_404_NOT_FOUND
     HTTP_CONFLICT = status.HTTP_409_CONFLICT
@@ -34,7 +34,7 @@ class SchemaErrorCodes(Enum):
 
 
 @unique
-class SchemaErrorMessages(Enum):
+class SchemaErrorMessages(StrEnum):
     SUBJECT_NOT_FOUND_FMT = "Subject '{subject}' not found."
     INVALID_COMPATIBILITY_LEVEL = (
         "Invalid compatibility level. Valid values are none, backward, "