Pass annotated origin type to build OpenAPI docs (#475)

* Pass annotated origin type to build OpenAPI docs

* Make Python 3.8 happy

blacksheep/server/openapi/v3.py

@@ -1,11 +1,16 @@
 import collections.abc as collections_abc
 import inspect
+import sys
 import warnings
 from abc import ABC, abstractmethod
 from dataclasses import dataclass, fields, is_dataclass
 from datetime import date, datetime
 from enum import Enum, IntEnum
 from typing import Any, Dict, Iterable, List, Optional, Tuple, Type, Union
+
+if sys.version_info >= (3, 9):
+    from typing import _AnnotatedAlias as AnnotatedAlias
+
 from typing import _GenericAlias as GenericAlias
 from typing import get_type_hints
 from uuid import UUID
@@ -649,6 +654,11 @@ def _get_schema_by_type(
         if stored_ref:  # pragma: no cover
             return stored_ref
 
+        if sys.version_info >= (3, 9):
+            if isinstance(object_type, AnnotatedAlias):
+                # Replace Annotated object type with the original type
+                object_type = getattr(object_type, "__origin__")
+
         if self._can_handle_class_type(object_type):
             return self._get_schema_for_class(object_type)