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

@@ -14,6 +14,7 @@
 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
 
@@ -39,12 +40,6 @@ 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
 
@@ -60,10 +55,8 @@ def jsondict(self, **kw):
         # .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))
+        # We provide json seralizable dict (super inefficiently).
+        return jsonable_encoder(self.dict(**kw))
 
 
 def get_or_create_state(*, state: object, key: str, factory: Callable[[], Any]) -> Any: