Support ChatGLM for "Summarize diff automatically"

Related issue: https://jihulab.com/gitlab-cn/gitlab/-/issues/3170

Upstream no longer supports the triggering method of quick action (!1786 (merged));

Now use automatic trigger, when MR is newly created, or when MR has a commit update.

What does this MR do and why?

About Page: https://about.gitlab.com/blog/2023/04/20/merge-request-changes-summary-ai/

Related upstream MR：

• Resolve "Auto-generate change summaries"
• Remove summarize diff quick action
• FE: Added summary notes drawer to merge requests

Screenshots or screen recordings

Trigger button

Show details

How to set up and validate locally

• Simulate a SaaS instance
• Create a Project and MRs under a Ultimate Group
• Feature.enable(:openai_experimentation)
• Feature.enable(:ai_related_settings, namespace)
• namespace.update!(experiment_features_enabled: true)
• Feature.enable(:summarize_diff_quick_action, user)
• Feature.enable(:summarize_diff_automatically, project)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.