Support GigaChat model from LangChain

[Rai220]

Describe the feature or potential improvement

I have an warning while using GigaChat model with LangChain:

Langfuse was not able to parse the LLM model. The LLM call will be recorded without model name. Please create an issue so we can fix your integration: https://github.com/langfuse/langfuse/issues/new/choose

Please support this type of models, it works just like gpt-3.5 (instructed with functions).

Additional information

https://python.langchain.com/docs/integrations/chat/gigachat/