Backend: Enable Hybrid Configuration for All Supported Duo Features Using Self-Hosted Models or Default GL AI Vendor Model

This issue is to capture requirements for hybrid configuration (a mix of both Self-Hosted and GitLab AI Vendor models) when using GitLab Duo Self-Hosted on a cloud license.

Previous (disabled) iteration of hybrid was only supported for Code Suggestions. Once a self-hosted AIG has been configured with the GitLab instance, the Chat feature could/would only route to the self-hosted AIG and therefore the self-hosted models.

The iteration will focus on enabling customers to choose from among their self-hosted models and the default GitLab AI Vendor model via the cloud-connector AI Gateway.

Definition of Done

• Self-Hosted customers have the ability to switch between models supported on their Self-Hosted environment OR the default GitLab AI Vendor models on a feature by feature basis
• Customers can choose one model per feature/sub-feature at the instance level, either:
  • a single model from among their hosted and configured models and available via their self-hosted AIG
  • the default GL AI Vendor model available on GitLab.com via the CC AIG
  • disable the feature
• for each Duo feature not supported by Self-Hosted (e.g. Code Review)
  • select the default GL AI Vendor model available on GitLab.com via the CC AIG