[Corrective Action] Document provider failover strategy for Anthropic-on-Vertex to Anthropic.

Problem to solve

During the 2024-11-15: GitLab Duo Chat failing on staginin... (gitlab-com/gl-infra/production#18860 - closed) • Alex Hanselka, two members were looking through our runbook to see where we had documented how to quickly fallback on provider given a degradation in service existing. We knew the process but only through a little bit of tribal knowledge managed to quickly do the procedure to fail to Anthropic as a provider.

Proposal

Document the process of Implement emergency fallback model switch via e... (gitlab-org/gitlab#480825 - closed) • Alejandro Rodríguez • 17.6 • Needs attention with the AI-gateway runbook.