Add support for Claude 3.5 Sonnet for code generation

What does this MR do and why?

Add support for Claude 3.5 Sonnet for code generation

Changelog: added

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. Set claude_3_5_code_generation_sonnet feature flag to true
2. Send a code suggestion request to api/v4/code_suggestions/completions with intent=generation
3. Response should have model.name: "claude-3-5-sonnet-20240620"

Resolves #468929 (closed)