[FF] `chatgpt_oauth_sign_in` -- Roll out ChatGPT OAuth sign-in button visibility

## Summary This issue is to roll out [the ChatGPT OAuth sign-in feature](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/239762) on production, that is currently behind the `chatgpt_oauth_sign_in` feature flag. ## Owners - Most appropriate Slack channel to reach out to: `#g_authentication` - Best individual to reach out to: @leetickett ## Expectations ### What are we expecting to happen? When the feature flag is enabled, the ChatGPT OAuth sign-in button will appear on the login page for instances that have configured the ChatGPT OAuth provider. The button is currently hidden by default behind this feature flag. A query parameter override (`?enable_chatgpt=true`) allows the button to be displayed even when the feature flag is disabled, for testing purposes. ### What can go wrong and how would we detect it? The ChatGPT button could appear on instances where it is not intended. This would be visible on the sign-in page. No data loss or stability impact is expected as this only controls UI visibility of an OAuth button. ## Rollout Steps Note: Please make sure to run the chatops commands in the Slack channel that gets impacted by the command. ### Rollout on non-production environments - Verify the MR with the feature flag is merged to `master` and has been deployed to non-production environments with `/chatops gitlab run auto_deploy status <merge-commit-of-your-feature>` - [ ] Enable the feature globally on non-production environments with `/chatops gitlab run feature set chatgpt_oauth_sign_in true --dev --pre --staging --staging-ref` - [ ] Verify that the ChatGPT sign-in button appears on the login page when the provider is configured. - [ ] If the feature flag causes end-to-end tests to fail, disable the feature flag on staging to avoid blocking [deployments](https://about.gitlab.com/handbook/engineering/deployments-and-releases/deployments/). ### Before production rollout - [ ] Ensure the MR has been deployed to both canary and production with `/chatops gitlab run auto_deploy status <merge-commit-of-your-feature>` ### Production rollout - [ ] Enable the feature globally on production with `/chatops gitlab run feature set chatgpt_oauth_sign_in true` - [ ] Verify that the ChatGPT sign-in button appears correctly on production. ### Cleanup - [ ] Remove the `chatgpt_oauth_sign_in` feature flag and the `chatgpt_oauth_hidden?` method in `AuthHelper`, ensuring the ChatGPT provider flows through `enabled_button_based_providers` without gating. - [ ] Remove the feature flag YAML definition file. --- 🤖 *This content was generated by GitLab Duo.*

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