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/human_approval.ipynb

@@ -159,7 +159,7 @@
    "outputs": [],
    "source": [
     "from langchain.agents import AgentType, initialize_agent, load_tools\n",
-    "from langchain_community.llms import OpenAI"
+    "from langchain_openai import OpenAI"
    ]
   },
   {