Allow extra fields in the config

Right now we cannot add extra fields to the config without it not being
backwards compatible.  Should follow the rules of protobuf here where
you can add new fields but they must be optional.

astacus/common/utils.py

@@ -14,14 +14,14 @@
 from contextlib import contextmanager
 from multiprocessing.dummy import Pool  # fastapi + fork = bad idea
 from pathlib import Path
+from fastapi.encoders import jsonable_encoder
 from pydantic import BaseModel
 from typing import Any, AsyncIterable, Callable, Dict, Final, Iterable, Optional, TypeVar, Union
 
 import asyncio
 import datetime
 import httpcore
 import httpx
-import json as _json
 import logging
 import os
 import re
@@ -39,12 +39,6 @@ class Config:
         # enumname.value (it is also slightly less safe but oh well)
         use_enum_values = True
 
-        # Extra values should be errors, as they are most likely typos
-        # which lead to grief when not detected. However, if we ever
-        # start deprecating some old fields and not wanting to parse
-        # them, this might need to be revisited.
-        extra = "forbid"
-
         # Validate field default values too
         validate_all = True
 
@@ -54,16 +48,8 @@ class Config:
         # possibly the tests themselves are broken
 
     def jsondict(self, **kw):
-        # By default,
-        #
-        # .json() returns json string.
-        # .dict() returns Python dict, but it has things that are not
-        # json serializable.
-        #
-        # We provide json seralizable dict (super inefficiently) here.
-        #
-        # This is mostly used for test code so that should be fine
-        return _json.loads(self.json(**kw))
+        """Serialize as a json encodable dict, eg datetimes become strings."""
+        return jsonable_encoder(self.dict(**kw))
 
 
 def get_or_create_state(*, state: object, key: str, factory: Callable[[], Any]) -> Any: