docs: langchain-openai (#15513)

Updates docs and cookbooks to import ChatOpenAI, OpenAI, and OpenAI
Embeddings from `langchain_openai`

There are likely more

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Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

cookbook/meta_prompt.ipynb

@@ -59,7 +59,7 @@
     "from langchain.chains import LLMChain\n",
     "from langchain.memory import ConversationBufferWindowMemory\n",
     "from langchain.prompts import PromptTemplate\n",
-    "from langchain_community.llms import OpenAI"
+    "from langchain_openai import OpenAI"
    ]
   },
   {