community[minor]: Adds Llamafile as an LLM (#17431)
* **Description:** Adds a simple LLM implementation for interacting with
[llamafile](https://github.com/Mozilla-Ocho/llamafile)-based models.
* **Dependencies:** N/A
* **Issue:** N/A
**Detail**
[llamafile](https://github.com/Mozilla-Ocho/llamafile) lets you run LLMs
locally from a single file on most computers without installing any
dependencies.
To use the llamafile LLM implementation, the user needs to:
1. Download a llamafile e.g.
https://huggingface.co/jartine/TinyLlama-1.1B-Chat-v1.0-GGUF/resolve/main/TinyLlama-1.1B-Chat-v1.0.Q5_K_M.llamafile?download=true
2. Make the file executable.
3. Run the llamafile in 'server mode'. (All llamafiles come packaged
with a lightweight server; by default, the server listens at
`http://localhost:8080`.)
```bash
wget https://url/of/model.llamafile
chmod +x model.llamafile
./model.llamafile --server --nobrowser
```
Now, the user can invoke the LLM via the LangChain client:
```python
from langchain_community.llms.llamafile import Llamafile
llm = Llamafile()
llm.invoke("Tell me a joke.")
```
