Refactor Anthropic import to langchain_anthropic and update model to …

…v3 (langchain-ai#524)

- Transition Anthropic API import to the langchain_anthropic package for
enhanced compatibility.
- Upgrade the AI model to claude-3-sonnet-20240229 for improved
performance and features.

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

examples/chat_playground/server.py

@@ -5,7 +5,7 @@
 from typing import List, Union
 
 from fastapi import FastAPI
-from langchain.chat_models import ChatAnthropic
+from langchain_anthropic.chat_models import ChatAnthropic
 from langchain_core.messages import AIMessage, HumanMessage, SystemMessage
 from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
 
@@ -27,7 +27,7 @@
     ]
 )
 
-chain = prompt | ChatAnthropic(model="claude-2")
+chain = prompt | ChatAnthropic(model_name="claude-3-sonnet-20240229")
 
 
 class InputChat(BaseModel):