Change summarize notes model

What does this MR do and why?

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/407785

I noticed that we were using the text-davinci-003 model for summarizing notes. gpt-3.5-turbo performs the same but at 10% the price per token and is recommend by OpenAi for most completions.

https://platform.openai.com/docs/guides/chat/chat-vs-completions

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