New LLM integration: Ctranslate2 (#10400)
## Description:
I've integrated CTranslate2 with LangChain. CTranlate2 is a recently
popular library for efficient inference with Transformer models that
compares favorably to alternatives such as HF Text Generation Inference
and vLLM in
[benchmarks](https://hamel.dev/notes/llm/inference/03_inference.html).
