docs, templates: update schema imports to core (#17885)

- chat models, messages
- documents
- agentaction/finish
- baseretriever,document
- stroutputparser
- more messages
- basemessage
- format_document
- baseoutputparser

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Co-authored-by: Bagatur <baskaryan@gmail.com>

templates/retrieval-agent/retrieval_agent/chain.py

@@ -5,13 +5,14 @@ from langchain.agents import AgentExecutor
 from langchain.agents.format_scratchpad import format_to_openai_function_messages
 from langchain.agents.output_parsers import OpenAIFunctionsAgentOutputParser
 from langchain.callbacks.manager import CallbackManagerForRetrieverRun
-from langchain.schema import BaseRetriever, Document
 from langchain.tools.retriever import create_retriever_tool
 from langchain_community.tools.convert_to_openai import format_tool_to_openai_function
 from langchain_community.utilities.arxiv import ArxivAPIWrapper
+from langchain_core.documents import Document
 from langchain_core.messages import AIMessage, HumanMessage
 from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
 from langchain_core.pydantic_v1 import BaseModel, Field
+from langchain_core.retrievers import BaseRetriever
 from langchain_openai import AzureChatOpenAI