Enable summarize_code_review_claude_3_7_sonnet feature flag by default

What does this MR do and why?

• Given the work done on this issue: Self-managed support and access control (unit p... (#495657 - closed), the summarize code review feature is available for self-managed instance.
• This MR enables the summarize_code_review_claude_3_7_sonnet feature flag by default to ensure self-managed instances also get to use the latest AI model, Claude 3.7 Sonnet.
• Additional context: #521383 (comment 2385465567)

MR acceptance checklist

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Related to #521383 (closed)