Move AI expanded logging functionality from the feature flag to an AI settings column

Description

Curretly enabling expanded logs setting in the page /admin/gitlab_duo/ just enable/disable the expanded_ai_logging FF.

Goal:

Decoupled the expanded_ai_logging FF from the instance configuration setting.

Implementation proposal

1. Create a new column in the ai_settings table.
2. Adapt the application setting model to point to the new column.
3. Implement it by passing the config in the headers of requests of to the AIGW the same way the FF does.

⚠️ while implementing this. Make sure it plays nice with the FF. The goal is not to roll out the FF! (Context here)

Definition of Done:

• Move AI expanded logging functionality from the feature flag to an AI settings column