[gitlab-org/gitlab] Rollout: expanded_external_authorization_permissions feature flag

### ROOT CAUSE The rollout of the `expanded_external_authorization_permissions` feature flag is incomplete and lacks proper testing. The feature flag controls the use of expanded permission groups, but the rollout plan is incomplete, and the current default behavior (disabled) may not align with the intended rollout strategy. This could lead to unexpected regressions if enabled prematurely or without verification. ### CODE FIX To properly rollout the feature flag, update the `config/feature_flags.yml` or the relevant codebase section to enable the flag in the target environment (e.g., staging). Then, implement a verification step to ensure no regressions occur. For example, in the GitLab codebase, modify the feature flag configuration to enable it and add a test case to validate the expanded permissions. ```yaml # config/feature_flags.yml expanded_external_authorization_permissions: enabled: true # Enable for staging ``` Additionally, ensure the rollout includes: 1. Enabling the flag on staging. 2. Running automated tests to verify compatibility. 3. Monitoring production for any issues post-rollout. If the issue involves specific code changes, consult the `config/authz/permission_groups/internal/project/external_authorization.yml` file to ensure the expanded permissions are correctly integrated.