Update Code Creation Slash Commands to Claude 3.7 Sonnet

Anthropic has released a new version of Claude Sonnet (3.7) which is supposed to have better code generation capabilities

We should update our existing code creation slash commands to this model using a feature flag

• /explain
• /fix
• /tests
• /refactor

Depends on AIGW Issue being resolved first gitlab-org/modelops/applied-ml/code-suggestions/ai-assist#807 (closed)