community[minor]: Integration for Friendli LLM and ChatFriendli ChatModel. (#17913)

## Description
- Add [Friendli](https://friendli.ai/) integration for `Friendli` LLM
and `ChatFriendli` chat model.
- Unit tests and integration tests corresponding to this change are
added.
- Documentations corresponding to this change are added.

## Dependencies
- Optional dependency
[`friendli-client`](https://pypi.org/project/friendli-client/) package
is added only for those who use `Frienldi` or `ChatFriendli` model.

## Twitter handle
- https://twitter.com/friendliai

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

@@ -0,0 +1,105 @@
+"""Test Friendli chat API."""
+
+import pytest
+from langchain_core.messages.ai import AIMessage
+from langchain_core.messages.human import HumanMessage
+from langchain_core.outputs.generation import Generation
+from langchain_core.outputs.llm_result import LLMResult
+
+from langchain_community.chat_models.friendli import ChatFriendli
+
+
+@pytest.fixture
+def friendli_chat() -> ChatFriendli:
+    """Friendli LLM for chat."""
+    return ChatFriendli(temperature=0, max_tokens=10)
+
+
+def test_friendli_call(friendli_chat: ChatFriendli) -> None:
+    """Test call."""
+    message = HumanMessage(content="What is generative AI?")
+    output = friendli_chat([message])
+    assert isinstance(output, AIMessage)
+    assert isinstance(output.content, str)
+
+
+def test_friendli_invoke(friendli_chat: ChatFriendli) -> None:
+    """Test invoke."""
+    output = friendli_chat.invoke("What is generative AI?")
+    assert isinstance(output, AIMessage)
+    assert isinstance(output.content, str)
+
+
+async def test_friendli_ainvoke(friendli_chat: ChatFriendli) -> None:
+    """Test async invoke."""
+    output = await friendli_chat.ainvoke("What is generative AI?")
+    assert isinstance(output, AIMessage)
+    assert isinstance(output.content, str)
+
+
+def test_friendli_batch(friendli_chat: ChatFriendli) -> None:
+    """Test batch."""
+    outputs = friendli_chat.batch(["What is generative AI?", "What is generative AI?"])
+    for output in outputs:
+        assert isinstance(output, AIMessage)
+        assert isinstance(output.content, str)
+
+
+async def test_friendli_abatch(friendli_chat: ChatFriendli) -> None:
+    """Test async batch."""
+    outputs = await friendli_chat.abatch(
+        ["What is generative AI?", "What is generative AI?"]
+    )
+    for output in outputs:
+        assert isinstance(output, AIMessage)
+        assert isinstance(output.content, str)
+
+
+def test_friendli_generate(friendli_chat: ChatFriendli) -> None:
+    """Test generate."""
+    message = HumanMessage(content="What is generative AI?")
+    result = friendli_chat.generate([[message], [message]])
+    assert isinstance(result, LLMResult)
+    generations = result.generations
+    assert len(generations) == 2
+    for generation in generations:
+        gen_ = generation[0]
+        assert isinstance(gen_, Generation)
+        text = gen_.text
+        assert isinstance(text, str)
+        generation_info = gen_.generation_info
+        if generation_info is not None:
+            assert "token" in generation_info
+
+
+async def test_friendli_agenerate(friendli_chat: ChatFriendli) -> None:
+    """Test async generate."""
+    message = HumanMessage(content="What is generative AI?")
+    result = await friendli_chat.agenerate([[message], [message]])
+    assert isinstance(result, LLMResult)
+    generations = result.generations
+    assert len(generations) == 2
+    for generation in generations:
+        gen_ = generation[0]
+        assert isinstance(gen_, Generation)
+        text = gen_.text
+        assert isinstance(text, str)
+        generation_info = gen_.generation_info
+        if generation_info is not None:
+            assert "token" in generation_info
+
+
+def test_friendli_stream(friendli_chat: ChatFriendli) -> None:
+    """Test stream."""
+    stream = friendli_chat.stream("Say hello world.")
+    for chunk in stream:
+        assert isinstance(chunk, AIMessage)
+        assert isinstance(chunk.content, str)
+
+
+async def test_friendli_astream(friendli_chat: ChatFriendli) -> None:
+    """Test async stream."""
+    stream = friendli_chat.astream("Say hello world.")
+    async for chunk in stream:
+        assert isinstance(chunk, AIMessage)
+        assert isinstance(chunk.content, str)