Update Duo Core settings for Self-Hosted customers

What does this MR do and why?

Currently, the Duo Core toggle is available to GitLab Duo Self-Hosted customers even though Duo Core is not currently supported with Duo Self-Hosted models. This poses the following issues:

• For Duo Self-Hosted customers with an offline license: this setting is misleading.
• For Duo Self-Hosted customers with an online license: Duo Core support is not available with Duo Self-Hosted models. To enable Duo Core at this state requires the use of the GitLab AI vendor model, which routes data to GitLab.com AI Gateway.

This MR updates this setting such that:

• For Duo Self-Hosted customers with an offline license: Duo Core setting checkbox is disabled.
• For Duo Self-Hosted customers with an online license and existing self hosted models: Selecting the Duo Core checkbox opens up a modal warning customers of the use of the GitLab AI vendor model under the hood.

References

Disable Core for Self-Hosted When No CC AIG Det... (#560442 - closed)

Screenshots or screen recordings

Description	Screenshot	Steps
Group configuration		Run GDK on SAAS mode: GITLAB_SIMULATE_SAAS=1 gdk start. Run the following script to setup a namespace with Duo: GITLAB_SIMULATE_SAAS=1 bundle exec 'rake gitlab:duo:setup' . Go to /groups/gitlab-duo/-/settings/gitlab_duo/configuration . Note there are no changes to the Duo Core setting.
Self-managed		Run GDK on non-SAAS mode: GITLAB_SIMULATE_SAAS=0 gdk start. Mock this method in ai_configuration_presenter: def can_manage_self_hosted_models? false end Go to /admin/gitlab_duo/configuration . Note there are no changes to the Duo Core setting.
Duo Self-Hosted with online license	demo.mov	With an online license, run GDK on non-SAAS mode: GITLAB_SIMULATE_SAAS=0 gdk start. Run the following setup script to get Duo Enterprise add on: GITLAB_SIMULATE_SAAS=0 bundle exec 'rake gitlab:duo:setup[duo_enterprise]'. Go to /admin/gitlab_duo/configuration . Note that a modal pops up on checkbox selection. The checkbox should not be selected unless the primary action button in the modal is clicked. The modal should not be displayed when the checkbox is unchecked (upon disabling Duo Core).
Duo Self-Hosted with offline license		You will need an offline license only. Or you can mock the following method in ai_configuration_presenter: def has_online_license? false end Run GDK on non-SAAS mode: GITLAB_SIMULATE_SAAS=0 gdk start. Run the following setup script to get Duo Enterprise add on: GITLAB_SIMULATE_SAAS=0 bundle exec 'rake gitlab:duo:setup[duo_enterprise]' . Go to /admin/gitlab_duo/configuration . Duo Core setting is disabled/greyed out with tooltip mentioning access to GitLab AI Gateway is required.

How to set up and validate locally

Refer to screen recording section with steps on how to validate each case locally.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.