Migrate Code Review Summary prompt to AIGW

Vitali Tatarintevrequested to merge
ck3g-use-aigw-prompt-for-summarize-review into master

What does this MR do and why?

Migrate code review summary to use AIGW prompt.

Summarize Review prompt was migrate some time ago #495131 (closed), but Duo Code Review still using legacy prompt.

References

Contributes to #501321 (closed)

How to set up and validate locally

  1. In rails console enable the feature flag 
    Feature.enable(:prompt_migration_review_merge_request)
  2. From your GDK directory run gdk tail gitlab-ai-gateway to watch AIGW logs
  3. Visit http://gdk.test:3000/gitlab-duo/test/-/merge_requests/1 and request review
  4. GitLab Duo should provide review summary
  5. Logs should show something like (slightly truncated):
2025-06-05_14:28:58.81672 gitlab-ai-gateway       : 2025-06-05 16:28:58 [info     ] Returning prompt from the registry correlation_id=1 prompt_id=summarize_review/base prompt_name='Claude 3.7 Summarize Review' prompt_version=2.0.0

2025-06-05_14:29:02.62132 gitlab-ai-gateway       : 2025-06-05 16:29:02 [info     ] 127.0.0.1:51467 - "POST /v1/prompts/summarize_review HTTP/1.1" 200 client_ip=127.0.0.1 client_port=51467 content_type=application/json correlation_id=1 cpu_s=0.02 duration_request=0.30614709854125977 duration_s=3.824813915998675 enabled-instance-verbose-ai-logs=False enabled_feature_flags= first_chunk_duration_s=3.8247983750188723 gitlab_feature_enabled_by_namespace_ids=1000000 gitlab_feature_enablement_type=duo_enterprise gitlab_global_user_id='' gitlab_host_name=gdk.test gitlab_instance_id=123 gitlab_language_server_version=None gitlab_realm=saas gitlab_saas_duo_pro_namespace_ids=None gitlab_version=18.1.0 http_version=1.1 meta.feature_category=ai_abstraction_layer method=POST path=/v1/prompts/summarize_review status_code=200 url=http://127.0.0.1:5052/v1/prompts/summarize_review user_agent=Ruby

POST /v1/prompts/summarize_review indicates that request went to the prompt endpoint.

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