feat(core): add Mistral AI support

[sachinkum0009]

Integrate langchain-mistralai and update configuration schemas to support Mistral models and embeddings.

Purpose

• Purpose is to support the LLMs from MistralAI

Proposed Changes

What does this PR add, remove or fix?

• This PR adds the support for mistral ai llms

Issues

• Links to relevant issues

Testing

• How was it tested, what were the results?

Updated the test based on the changes. My system is using python 3.12, which is giving errors when running the pytest.

[maciejmajek]

Hi @sachinkum0009, apologies for long review time. I'm on vacation atm, will take a look early next week. Thanks!

[sachinkum0009]

Thanks @maciejmajek

I found out that we don't need to add langchain-mistralai to use mistralai. Since it uses the OpenAI API, we can update the config.toml to call the mistralai models

[openai]
simple_model = "mistral-small-latest"
complex_model = "mistral-small-2506"
embeddings_model = "mistral-embed"
base_url = "https://api.mistral.ai/v1/"

What is your opinion on this?
Also, we can update the docs of rai to demonstrate the mistralai usecase.