Use group namespace settings for Summarize my code review

What does this MR do and why?

Implements Connect summarize my merge request review to na... (#409537 - closed) for Add Summarize my code review editor action (!118807 - merged).

For references please look at Add namespace settings around AI features (!118222 - merged).

How to set up and validate locally

1. Enable feature flags:

Feature.enable(:openai_experimentation)
Feature.enable(:ai_experimentation_api)
Feature.enable(:summarize_my_code_review)
Feature.enable(:ai_related_settings)

1. Enable GitLab SaaS for your GDK
2. In admin section, change plan of one group to Ultimate.
3. In Group edit page, under Settings > General > Permissions and group features enable these settings:
   1. Use third-party AI services
   2. Use experiment features
4. Open any merge request in a project within that group
5. You should now see a Summarize My Code Review actions in the editor at the bottom of the page: