[Integration] NVIDIA AI Playground (#14648)

Description: Added NVIDIA AI Playground Initial support for a selection of models (Llama models, Mistral, etc.)

Dependencies: These models do depend on the AI Playground services in NVIDIA NGC. API keys with a significant amount of trial compute are available (10K queries as of the time of writing).

H/t to @VKudlay

docs/docs/integrations/providers/nv_aiplay.mdx

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+# NVIDIA AI Playground
+
+> [NVIDIA AI Playground](https://www.nvidia.com/en-us/research/ai-playground/) gives users easy access to hosted endpoints for generative AI models like Llama-2, Mistral, etc. This example demonstrates how to use LangChain to interact with supported AI Playground models.
+
+These models are provided via the `langchain-nvidia-aiplay` package.
+
+## Installation
+
+```bash
+pip install -U langchain-nvidia-aiplay
+```
+
+## Setup and Authentication
+
+- Create a free account at [NVIDIA GPU Cloud](https://catalog.ngc.nvidia.com/).
+- Navigate to `Catalog > AI Foundation Models > (Model with API endpoint)`.
+- Select `API` and generate the key `NVIDIA_API_KEY`.
+
+```bash
+export NVIDIA_API_KEY=nvapi-XXXXXXXXXXXXXXXXXXXXXXXXXX
+```
+
+```python
+from langchain_nvidia_aiplay import ChatNVAIPlay
+
+llm = ChatNVAIPlay(model="mixtral_8x7b")
+result = llm.invoke("Write a ballad about LangChain.")
+print(result.content)
+```
+
+## Using NVIDIA AI Playground Models
+
+A selection of NVIDIA AI Playground models are supported directly in LangChain with familiar APIs.
+
+The active models which are supported can be found [in NGC](https://catalog.ngc.nvidia.com/orgs/nvidia/teams/ai-foundation/). In addition, a selection of models can be retrieved from `langchain.<llms/chat_models>.nv_aiplay` which pull in default model options based on their use cases. 
+
+**The following may be useful examples to help you get started:**
+- **[`ChatNVAIPlay` Model](/docs/integrations/chat/nv_aiplay).**
+- **[`NVAIPlayEmbedding` Model for RAG Workflows](/docs/integrations/text_embeddings/nv_aiplay).**