Convert global_search_code_tab to admin settings

Background

As a part of our initiative to reduce FFs in search team interna-link we plan to convert all global_search__tab ops feature flag we to admin settings.

Proposal

• MR1: Create a global_search_settings column
• MR2: Backfill the data in the column
• MR3: Create and Implement the logic to store and retrieve global_search_code_tab setting.
• MR4: Update the frontend to respect this admin setting instead of the feature flag.
• MR5: Remove Feature Flag.
• MR6: Update the documentation.

The MR3 and MR4 can be chained and deployed together.