examples: updated deprecated imports (#3602)

examples/langchain-python-rag-document/main.py

-from langchain.document_loaders import OnlinePDFLoader
-from langchain.vectorstores import Chroma
-from langchain.embeddings import GPT4AllEmbeddings
-from langchain import PromptTemplate
-from langchain.llms import Ollama
+from langchain_community.document_loaders import OnlinePDFLoader
+from langchain_community.vectorstores import Chroma
+from langchain_community.embeddings import GPT4AllEmbeddings
+from langchain_core.prompts import PromptTemplate
+from langchain_community.llms import Ollama
 from langchain.callbacks.manager import CallbackManager
 from langchain.callbacks.streaming_stdout import StreamingStdOutCallbackHandler
 from langchain.chains import RetrievalQA