update env sample

Author: James N.

voice_agent/app/backend/.env.sample

@@ -1,7 +1,6 @@
 
 AZURE_OPENAI_ENDPOINT="https://.openai.azure.com/"
 AZURE_OPENAI_API_KEY=
-AZURE_OPENAI_CHAT_DEPLOYMENT=gpt-4o-mini
 AZURE_OPENAI_EMB_ENDPOINT= [Optional] if different from your realtime endpoint
 AZURE_OPENAI_EMB_API_KEY= [Optional] if providing an embedding endpoint
 AZURE_OPENAI_EMB_DEPLOYMENT="text-embedding-ada-002"
@@ -18,4 +17,4 @@ TURN_DETECTION_THRESHOLD=0.5
 TURN_DETECTION_PREFIX_PADDING_MS=300
 TURN_DETECTION_SILENCE_DURATION_MS=200
 AZURE_REDIS_ENDPOINT=#optional, if you want to use redis for caching which support distributed caching for high
-AZURE_REDIS_KEY=
+AZURE_REDIS_KEY=#optional, if you want to use redis for caching which support distributed caching for high