support for anthropic models on vertex

[jjallaire]

To use Anthropic models on Vertex, you can use the standard anthropic model provider with a vertex suffix (e.g. anthropic/vertex/claude-3-5-sonnet-v2@20241022). You should also set two environment variables indicating your project ID and region. Here is a complete example:

export ANTHROPIC_VERTEX_PROJECT_ID=project-12345
export ANTHROPIC_VERTEX_REGION=us-east5
inspect eval ctf.py --model anthropic/vertex/claude-3-5-sonnet-v2@20241022