docs(event-handler): add docstring for serializer in BedrockAgentFunctionResolver (#7808)

Co-authored-by: Leandro Damascena <lcdama@amazon.pt>

Author: dreamorosi

aws_lambda_powertools/event_handler/bedrock_agent_function.py

@@ -133,6 +133,12 @@ def lambda_handler(event, context):
     context: dict
 
     def __init__(self, serializer: Callable | None = None) -> None:
+        """
+        Parameters
+        ----------
+        serializer: Callable, optional
+            function to serialize `obj` to a JSON formatted `str`, by default json.dumps
+        """
         self._tools: dict[str, dict[str, Any]] = {}
         self.current_event: BedrockAgentFunctionEvent | None = None
         self.context = {}