community[minor]: Dappier chat model integration (#19370)

**Description:** 

This PR adds [Dappier](https://dappier.com/) for the chat model. It
supports generate, async generate, and batch functionalities. We added
unit and integration tests as well as a notebook with more details about
our chat model.


**Dependencies:** 
    No extra dependencies are needed.

libs/community/tests/integration_tests/chat_models/test_dappier.py

@@ -0,0 +1,58 @@
+from typing import List
+
+import pytest
+from langchain_core.messages import AIMessage, BaseMessage, HumanMessage
+from langchain_core.outputs import ChatGeneration, LLMResult
+
+from langchain_community.chat_models.dappier import (
+    ChatDappierAI,
+)
+
+
+@pytest.mark.scheduled
+def test_dappier_chat() -> None:
+    """Test ChatDappierAI wrapper."""
+    chat = ChatDappierAI(
+        dappier_endpoint="https://api.dappier.com/app/datamodelconversation",
+        dappier_model="dm_01hpsxyfm2fwdt2zet9cg6fdxt",
+    )
+    message = HumanMessage(content="Who are you ?")
+    response = chat([message])
+    assert isinstance(response, AIMessage)
+    assert isinstance(response.content, str)
+
+
+@pytest.mark.scheduled
+def test_dappier_generate() -> None:
+    """Test generate method of Dappier AI."""
+    chat = ChatDappierAI(
+        dappier_endpoint="https://api.dappier.com/app/datamodelconversation",
+        dappier_model="dm_01hpsxyfm2fwdt2zet9cg6fdxt",
+    )
+    chat_messages: List[List[BaseMessage]] = [
+        [HumanMessage(content="Who won the last super bowl?")],
+    ]
+    messages_copy = [messages.copy() for messages in chat_messages]
+    result: LLMResult = chat.generate(chat_messages)
+    assert isinstance(result, LLMResult)
+    for response in result.generations[0]:
+        assert isinstance(response, ChatGeneration)
+        assert isinstance(response.text, str)
+        assert response.text == response.message.content
+    assert chat_messages == messages_copy
+
+
+@pytest.mark.scheduled
+async def test_dappier_agenerate() -> None:
+    """Test async generation."""
+    chat = ChatDappierAI(
+        dappier_endpoint="https://api.dappier.com/app/datamodelconversation",
+        dappier_model="dm_01hpsxyfm2fwdt2zet9cg6fdxt",
+    )
+    message = HumanMessage(content="Who won the last super bowl?")
+    result: LLMResult = await chat.agenerate([[message], [message]])
+    assert isinstance(result, LLMResult)
+    for response in result.generations[0]:
+        assert isinstance(response, ChatGeneration)
+        assert isinstance(response.text, str)
+        assert response.text == response.message.content