feat: custom exceptions instead of direct fastapi.httpexceptions

Resolves #2

src/exceptions.py

@@ -1,3 +1,15 @@
 """
 Global exceptions
-"""
+"""
+from typing import Optional
+
+from fastapi import HTTPException, status
+
+
+class UnprocessableContent(HTTPException):
+	def __init__(self, message: Optional[str] = None) -> None:
+		detail = "Not authorized" if not message else message
+		super().__init__(
+			status_code=status.HTTP_422_UNPROCESSABLE_CONTENT,
+			detail=detail,
+		)