Rename code suggestions ops flag

What does this MR do and why?

Resolves #438096 (closed)

This MR renames the code_suggestions_tokens_api ops feature flag to ai_duo_code_suggestions_switch. This is more descriptive of the actual function of the ops feature flag.

This feature flag is default enabled, so we do not need intermediary step before changing the name.

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.

Screenshots or screen recordings

n/a

How to set up and validate locally

n/a

Related to #438096 (closed)