feat(schema): provide a way set _ignore_default_error to True (default to false)

_ignore_default_error will ignore errors like:

"Default value <null> must match first schema in union with type: null"

...which I agree are errors but are painful to fix when backporting stuff.

Author: qfritz

schema_registry/client/schema.py

@@ -69,6 +69,7 @@ class AvroSchema(BaseSchema):
     def __init__(self, *args: typing.Any, **kwargs: typing.Any) -> None:
         self._expanded_schema: typing.Optional[typing.Dict] = None
         self._flat_schema: typing.Optional[typing.Dict] = None
+        self._ignore_default_error: typing.Optional[bool] = False
 
         super().__init__(*args, **kwargs)
 
@@ -103,14 +104,14 @@ def flat_schema(self) -> typing.Dict:
             # NOTE: Dict expected when we pass a dict
             self._flat_schema = typing.cast(
                 typing.Dict,
-                fastavro.parse_schema(self.raw_schema, _write_hint=False, _force=True),
+                fastavro.parse_schema(self.raw_schema, _write_hint=False, _force=True, _ignore_default_error=self._ignore_default_error),
             )
 
         return self._flat_schema
 
     def parse_schema(self, schema: typing.Dict) -> typing.Dict:
         # NOTE: Dict expected when we pass a dict
-        return typing.cast(typing.Dict, fastavro.parse_schema(schema, _force=True))
+        return typing.cast(typing.Dict, fastavro.parse_schema(schema, _force=True, _ignore_default_error=True))
 
     @staticmethod
     def load(fp: str) -> AvroSchema: