Add index chat settings methods (get/update/reset) #1288

Meilisearch has index-level chat settings: GET, PATCH and DELETE on /indexes/{index_uid}/settings/chat:
https://www.meilisearch.com/docs/reference/api/settings/get-chat

The Python SDK has no dedicated methods for them. Python users currently need raw HTTP or update_settings({"chat": ...}).

Would get_chat_settings(), update_chat_settings(body) and reset_chat_settings() be welcome, following the existing settings-method conventions?

I have a patch and tests prepared using AI assistance. Local checks run by the AI assistant cover reading, updating, partial updates and resetting settings against Meilisearch 1.55.0 Community Edition. I haven't personally run those checks.