adds reporting of response time to explorer chat messages (microsoft#243

)

Shows up in the footer of the chat message:

![image](https://github.com/user-attachments/assets/e7822513-139c-4387-a935-4caf82bb2f21)

assistants/explorer-assistant/assistant/chat.py

@@ -7,6 +7,7 @@
 
 import logging
 import re
+import time
 from typing import Any, Awaitable, Callable
 
 import deepmerge
@@ -183,6 +184,9 @@ async def respond_to_conversation(
     # define the metadata key for any metadata created within this method
     method_metadata_key = "respond_to_conversation"
 
+    # track the start time of the response generation
+    response_start_time = time.time()
+
     # get the list of conversation participants
     participants_response = await context.get_participants(include_inactive=True)
 
@@ -371,13 +375,22 @@ async def respond_to_conversation(
                         },
                     )
 
+            # create the footer items for the response
             footer_items = []
+
             if completion is not None:
                 # get the total tokens used for the completion
                 completion_total_tokens = completion.usage.total_tokens if completion.usage else 0
                 footer_items.append(_get_token_usage_message(config.request_config.max_tokens, completion_total_tokens))
 
-            # add the completion to the metadata for debugging
+            # track the end time of the response generation
+            response_end_time = time.time()
+            response_duration = response_end_time - response_start_time
+
+            # add the response duration to the footer items
+            footer_items.append(_get_response_duration_message(response_duration))
+
+            # update the metadata with debug information
             deepmerge.always_merger.merge(
                 metadata,
                 {
@@ -593,6 +606,14 @@ async def _get_history_messages(
     return history
 
 
+def _get_response_duration_message(response_duration: float) -> str:
+    """
+    Generate a display friendly message for the response duration, to be added to the footer items.
+    """
+
+    return f"Response time: {response_duration:.2f} seconds"
+
+
 def _get_token_usage_message(
     max_tokens: int,
     completion_total_tokens: int,