Vulnerability Explanation AI Gateway Integration

Summary

Vulnerability Explanation needs to be integrated with the AI Gateway as part of our efforts to separate our direct GitLab code from the specific AI providers.

Blocker

At time of issue writing, the AI Gateway does not currently support Vertex, making this migration impossible. Once Vertex is supported, the migration should be straightforward due to the model agnostic writing of the AI Gateway client class in GitLab. workflowblocked by AI Gateway as the Sole Access Point for Monolit... (&13024) • Unassigned.

Implementation Plan

• Update the LLM Client for Vulnerability Explanation to use the new `AiGateway::Client` class.